* [PATCH v8 1/8] KVM: x86: Provide INVLPG linear address to intercept handlers
2026-09-23 14:02 [PATCH v8 0/8] KVM: nSVM: Enable DecodeAssists for nested guests Tina Zhang
@ 2026-09-23 14:02 ` Tina Zhang
2026-09-23 19:49 ` Jim Mattson
2026-09-23 14:02 ` [PATCH v8 2/8] KVM: nSVM: Synthesize DecodeAssists EXITINFO for emulated intercepts Tina Zhang
` (6 subsequent siblings)
7 siblings, 1 reply; 11+ messages in thread
From: Tina Zhang @ 2026-09-23 14:02 UTC (permalink / raw)
To: Sean Christopherson, Jim Mattson, kvm
Cc: Paolo Bonzini, Shuah Khan, zhouyanjing, linux-kselftest, linux-kernel
INVLPG's memory operand is decoded with NoAccess, and thus src_val does
not contain the operand address. Intercept handlers therefore cannot
construct exit state that reports the linear address from the existing
x86_instruction_info fields.
Add get_invlpg_linear_addr() to compute the address through __linearize(),
using the same flags as em_invlpg(), and pass the result through
x86_instruction_info.
Signed-off-by: Tina Zhang <zhang_wei@open-hieco.net>
---
arch/x86/kvm/emulate.c | 23 +++++++++++++++++++++++
arch/x86/kvm/kvm_emulate.h | 1 +
2 files changed, 24 insertions(+)
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index c1b21282187f..299aeaca6cf2 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -411,6 +411,9 @@ static int em_salc(struct x86_emulate_ctxt *ctxt)
_fault ? X86EMUL_UNHANDLEABLE : X86EMUL_CONTINUE; \
})
+static u64 get_invlpg_linear_addr(struct x86_emulate_ctxt *ctxt,
+ enum x86_intercept intercept);
+
static int emulator_check_intercept(struct x86_emulate_ctxt *ctxt,
enum x86_intercept intercept,
enum x86_intercept_stage stage)
@@ -428,6 +431,7 @@ static int emulator_check_intercept(struct x86_emulate_ctxt *ctxt,
.src_type = ctxt->src.type,
.dst_type = ctxt->dst.type,
.ad_bytes = ctxt->ad_bytes,
+ .invlpg_linear_addr = get_invlpg_linear_addr(ctxt, intercept),
.rip = ctxt->eip,
.next_rip = ctxt->_eip,
};
@@ -684,6 +688,25 @@ static __always_inline int __linearize(struct x86_emulate_ctxt *ctxt,
return emulate_gp(ctxt, 0);
}
+static u64 get_invlpg_linear_addr(struct x86_emulate_ctxt *ctxt,
+ enum x86_intercept intercept)
+{
+ unsigned int max_size;
+ unsigned long linear = 0;
+
+ if (intercept != x86_intercept_invlpg)
+ return 0;
+
+ /*
+ * Ignore faults, just as em_invlpg() does. Calling __linearize()
+ * exactly as em_invlpg() does guarantees agreement with
+ * em_invlpg() on the linear address.
+ */
+ __linearize(ctxt, ctxt->src.addr.mem, &max_size, 1, ctxt->mode,
+ &linear, X86EMUL_F_INVLPG);
+ return linear;
+}
+
static int linearize(struct x86_emulate_ctxt *ctxt,
struct segmented_address addr,
unsigned size, bool write,
diff --git a/arch/x86/kvm/kvm_emulate.h b/arch/x86/kvm/kvm_emulate.h
index 3e375af15c03..d05558ef28ae 100644
--- a/arch/x86/kvm/kvm_emulate.h
+++ b/arch/x86/kvm/kvm_emulate.h
@@ -51,6 +51,7 @@ struct x86_instruction_info {
u8 src_type; /* type of source operand */
u8 dst_type; /* type of destination operand */
u8 ad_bytes; /* size of src/dst address */
+ u64 invlpg_linear_addr; /* linear address, if INVLPG */
u64 rip; /* rip of the instruction */
u64 next_rip; /* rip following the instruction */
};
--
2.43.7
^ permalink raw reply [flat|nested] 11+ messages in thread* Re: [PATCH v8 1/8] KVM: x86: Provide INVLPG linear address to intercept handlers
2026-09-23 14:02 ` [PATCH v8 1/8] KVM: x86: Provide INVLPG linear address to intercept handlers Tina Zhang
@ 2026-09-23 19:49 ` Jim Mattson
0 siblings, 0 replies; 11+ messages in thread
From: Jim Mattson @ 2026-09-23 19:49 UTC (permalink / raw)
To: Tina Zhang
Cc: Sean Christopherson, kvm, Paolo Bonzini, Shuah Khan, zhouyanjing,
linux-kselftest, linux-kernel
On Wed, Sep 23, 2026 at 7:02 AM Tina Zhang <zhang_wei@open-hieco.net> wrote:
>
> INVLPG's memory operand is decoded with NoAccess, and thus src_val does
> not contain the operand address. Intercept handlers therefore cannot
> construct exit state that reports the linear address from the existing
> x86_instruction_info fields.
>
> Add get_invlpg_linear_addr() to compute the address through __linearize(),
> using the same flags as em_invlpg(), and pass the result through
> x86_instruction_info.
>
> Signed-off-by: Tina Zhang <zhang_wei@open-hieco.net>
Reviewed-by: Jim Mattson <jmattson@google.com>
^ permalink raw reply [flat|nested] 11+ messages in thread
* [PATCH v8 2/8] KVM: nSVM: Synthesize DecodeAssists EXITINFO for emulated intercepts
2026-09-23 14:02 [PATCH v8 0/8] KVM: nSVM: Enable DecodeAssists for nested guests Tina Zhang
2026-09-23 14:02 ` [PATCH v8 1/8] KVM: x86: Provide INVLPG linear address to intercept handlers Tina Zhang
@ 2026-09-23 14:02 ` Tina Zhang
2026-09-23 14:02 ` [PATCH v8 3/8] KVM: nSVM: Track valid hardware DecodeAssist bytes Tina Zhang
` (5 subsequent siblings)
7 siblings, 0 replies; 11+ messages in thread
From: Tina Zhang @ 2026-09-23 14:02 UTC (permalink / raw)
To: Sean Christopherson, Jim Mattson, kvm
Cc: Paolo Bonzini, Shuah Khan, zhouyanjing, linux-kselftest, linux-kernel
When the x86 emulator encounters an instruction intercepted by L1,
svm_check_intercept() synthesizes a nested VM-Exit without fresh hardware
DecodeAssist state. Populate the architectural EXITINFO1 field when
DecodeAssists is exposed to L1.
Provide the GPR number for MOV CR/DR, the interrupt vector for INTn, and
the linear address for INVLPG. Preserve the MOV-to-CR0 decode information
when a selective CR0 write intercept is triggered. Leave EXITINFO1 clear
for CLTS, LMSW, SMSW, and INVLPGA; the INVLPGA address remains in guest
rAX. Leave EXITINFO1 unchanged when DecodeAssists is not exposed, and
leave unrelated intercepts unchanged.
Signed-off-by: Tina Zhang <zhang_wei@open-hieco.net>
Reviewed-by: Jim Mattson <jmattson@google.com>
---
arch/x86/kvm/svm/svm.c | 27 +++++++++++++++++++++++++++
1 file changed, 27 insertions(+)
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index f5aa3d7d3a10..e83e4e5e7b93 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4837,6 +4837,7 @@ static int svm_check_intercept(struct kvm_vcpu *vcpu,
int vmexit, ret = X86EMUL_CONTINUE;
struct __x86_intercept icpt_info;
struct vmcb *vmcb = svm->vmcb;
+ bool decode_assists;
if (info->intercept >= ARRAY_SIZE(x86_intercept_map))
goto out;
@@ -4846,14 +4847,26 @@ static int svm_check_intercept(struct kvm_vcpu *vcpu,
if (stage != icpt_info.stage)
goto out;
+ decode_assists = guest_cpu_cap_has(vcpu, X86_FEATURE_DECODEASSISTS);
+
switch (icpt_info.exit_code) {
case SVM_EXIT_READ_CR0:
if (info->intercept == x86_intercept_cr_read)
icpt_info.exit_code += info->modrm_reg;
+
+ if (decode_assists)
+ vmcb->control.exit_info_1 =
+ info->intercept == x86_intercept_cr_read ?
+ CR_VALID | (info->modrm_rm & SVM_EXITINFO_REG_MASK) : 0;
break;
case SVM_EXIT_WRITE_CR0: {
unsigned long cr0, val;
+ if (decode_assists)
+ vmcb->control.exit_info_1 =
+ info->intercept == x86_intercept_cr_write ?
+ CR_VALID | (info->modrm_rm & SVM_EXITINFO_REG_MASK) : 0;
+
/*
* Adjust the exit code accordingly if a CR other than CR0 is
* being written, and skip straight to the common handling as
@@ -4898,6 +4911,20 @@ static int svm_check_intercept(struct kvm_vcpu *vcpu,
case SVM_EXIT_READ_DR0:
case SVM_EXIT_WRITE_DR0:
icpt_info.exit_code += info->modrm_reg;
+ if (decode_assists)
+ vmcb->control.exit_info_1 = info->modrm_rm & SVM_EXITINFO_REG_MASK;
+ break;
+ case SVM_EXIT_SWINT:
+ if (decode_assists)
+ vmcb->control.exit_info_1 = info->src_val & 0xff;
+ break;
+ case SVM_EXIT_INVLPG:
+ if (decode_assists)
+ vmcb->control.exit_info_1 = info->invlpg_linear_addr;
+ break;
+ case SVM_EXIT_INVLPGA:
+ if (decode_assists)
+ vmcb->control.exit_info_1 = 0;
break;
case SVM_EXIT_MSR:
if (info->intercept == x86_intercept_wrmsr)
--
2.43.7
^ permalink raw reply [flat|nested] 11+ messages in thread* [PATCH v8 3/8] KVM: nSVM: Track valid hardware DecodeAssist bytes
2026-09-23 14:02 [PATCH v8 0/8] KVM: nSVM: Enable DecodeAssists for nested guests Tina Zhang
2026-09-23 14:02 ` [PATCH v8 1/8] KVM: x86: Provide INVLPG linear address to intercept handlers Tina Zhang
2026-09-23 14:02 ` [PATCH v8 2/8] KVM: nSVM: Synthesize DecodeAssists EXITINFO for emulated intercepts Tina Zhang
@ 2026-09-23 14:02 ` Tina Zhang
2026-09-23 14:02 ` [PATCH v8 4/8] KVM: nSVM: Propagate hardware DecodeAssist bytes to VMCB12 Tina Zhang
` (4 subsequent siblings)
7 siblings, 0 replies; 11+ messages in thread
From: Tina Zhang @ 2026-09-23 14:02 UTC (permalink / raw)
To: Sean Christopherson, Jim Mattson, kvm
Cc: Paolo Bonzini, Shuah Khan, zhouyanjing, linux-kselftest, linux-kernel
VMCB02 instruction bytes are valid only for the hardware VM-Exit that
populated them. Track whether VMCB02 contains instruction bytes for the
data #PF or #NPF currently being reflected to L1 so that stale bytes are
not copied to VMCB12.
Invalidate VMCB02's instruction-byte state when preparing VMCB02,
normally in response to an emulated VMRUN. Mark the bytes as valid only
when the current VMCB02 exit is a data #PF or #NPF. Opcode exits and
instruction-fetch faults are excluded by inspecting the exit state.
A subsequent change will use this state when propagating hardware
DecodeAssist instruction bytes to VMCB12.
Signed-off-by: Tina Zhang <zhang_wei@open-hieco.net>
Reviewed-by: Jim Mattson <jmattson@google.com>
---
arch/x86/kvm/svm/nested.c | 38 +++++++++++++++++++++++++++++++++++++-
arch/x86/kvm/svm/svm.h | 3 +++
2 files changed, 40 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 82c49a24dd75..a87b88d8eeac 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -35,6 +35,35 @@
#define CC KVM_NESTED_VMENTER_CONSISTENCY_CHECK
+static void nested_svm_invalidate_insn_bytes(struct vmcb *vmcb)
+{
+ vmcb->control.insn_len = 0;
+}
+
+static bool nested_svm_vmexit_supports_insn_bytes(const struct vmcb *vmcb)
+{
+ u64 exit_code = vmcb->control.exit_code;
+
+ if (exit_code != SVM_EXIT_NPF &&
+ exit_code != SVM_EXIT_EXCP_BASE + PF_VECTOR)
+ return false;
+
+ return !(vmcb->control.exit_info_1 & PFERR_FETCH_MASK);
+}
+
+static void nested_svm_set_vmcb02_insn_bytes_valid(struct vcpu_svm *svm)
+{
+ svm->nested.vmcb02_insn_bytes_valid =
+ cpu_feature_enabled(X86_FEATURE_DECODEASSISTS) &&
+ nested_svm_vmexit_supports_insn_bytes(svm->nested.vmcb02.ptr);
+}
+
+static void nested_svm_invalidate_vmcb02_insn_bytes(struct vcpu_svm *svm)
+{
+ nested_svm_invalidate_insn_bytes(svm->nested.vmcb02.ptr);
+ svm->nested.vmcb02_insn_bytes_valid = false;
+}
+
static void nested_svm_inject_npf_exit(struct kvm_vcpu *vcpu,
struct x86_exception *fault,
bool from_hardware)
@@ -68,6 +97,10 @@ static void nested_svm_inject_npf_exit(struct kvm_vcpu *vcpu,
(fault->error_code & ~PFERR_GUEST_FAULT_STAGE_MASK);
vmcb->control.exit_info_2 = fault->address;
+ if (from_hardware)
+ nested_svm_set_vmcb02_insn_bytes_valid(svm);
+ else
+ nested_svm_invalidate_vmcb02_insn_bytes(svm);
nested_svm_vmexit(svm);
}
@@ -873,6 +906,7 @@ static void nested_vmcb02_prepare_control(struct vcpu_svm *svm)
* Filled at exit: exit_code, exit_info_1, exit_info_2, exit_int_info,
* exit_int_info_err, next_rip, insn_len, insn_bytes.
*/
+ nested_svm_invalidate_vmcb02_insn_bytes(svm);
if (guest_cpu_cap_has(vcpu, X86_FEATURE_VGIF) &&
(vmcb12_ctrl->int_ctl & V_GIF_ENABLE_MASK))
@@ -1653,8 +1687,10 @@ int nested_svm_exit_handled(struct vcpu_svm *svm)
vmexit = nested_svm_intercept(svm);
- if (vmexit == NESTED_EXIT_DONE)
+ if (vmexit == NESTED_EXIT_DONE) {
+ nested_svm_set_vmcb02_insn_bytes_valid(svm);
nested_svm_vmexit(svm);
+ }
return vmexit;
}
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index e958943b8162..1e12ef1105c0 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -243,6 +243,9 @@ struct svm_nested_state {
* on its side.
*/
bool force_msr_bitmap_recalc;
+
+ /* True if VMCB02 has instruction bytes for the current nested exit. */
+ bool vmcb02_insn_bytes_valid;
};
struct vcpu_sev_es_state {
--
2.43.7
^ permalink raw reply [flat|nested] 11+ messages in thread* [PATCH v8 4/8] KVM: nSVM: Propagate hardware DecodeAssist bytes to VMCB12
2026-09-23 14:02 [PATCH v8 0/8] KVM: nSVM: Enable DecodeAssists for nested guests Tina Zhang
` (2 preceding siblings ...)
2026-09-23 14:02 ` [PATCH v8 3/8] KVM: nSVM: Track valid hardware DecodeAssist bytes Tina Zhang
@ 2026-09-23 14:02 ` Tina Zhang
2026-09-23 14:02 ` [PATCH v8 5/8] KVM: nSVM: Fetch DecodeAssist bytes for synthesized faults Tina Zhang
` (3 subsequent siblings)
7 siblings, 0 replies; 11+ messages in thread
From: Tina Zhang @ 2026-09-23 14:02 UTC (permalink / raw)
To: Sean Christopherson, Jim Mattson, kvm
Cc: Paolo Bonzini, Shuah Khan, zhouyanjing, linux-kselftest, linux-kernel
DecodeAssists provides instruction bytes for nested page faults and
intercepted page faults caused by data accesses. When the feature is
exposed to L1, copy fresh hardware-provided instruction bytes from VMCB02
to VMCB12 for these exits.
Leave the VMCB12 instruction-byte state untouched when DecodeAssists is
not exposed. Otherwise, invalidate the state for instruction-fetch page
faults, unrelated exits, and exits without fresh hardware bytes.
Signed-off-by: Tina Zhang <zhang_wei@open-hieco.net>
Reviewed-by: Jim Mattson <jmattson@google.com>
---
arch/x86/kvm/svm/nested.c | 37 +++++++++++++++++++++++++++++++++++++
1 file changed, 37 insertions(+)
diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index a87b88d8eeac..e839f61211c9 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -40,6 +40,20 @@ static void nested_svm_invalidate_insn_bytes(struct vmcb *vmcb)
vmcb->control.insn_len = 0;
}
+static void nested_svm_copy_insn_bytes(struct vmcb *to,
+ const struct vmcb *from)
+{
+ u8 insn_len = from->control.insn_len;
+
+ if (WARN_ON_ONCE(insn_len > sizeof(from->control.insn_bytes))) {
+ nested_svm_invalidate_insn_bytes(to);
+ return;
+ }
+
+ memcpy(to->control.insn_bytes, from->control.insn_bytes, insn_len);
+ to->control.insn_len = insn_len;
+}
+
static bool nested_svm_vmexit_supports_insn_bytes(const struct vmcb *vmcb)
{
u64 exit_code = vmcb->control.exit_code;
@@ -64,6 +78,27 @@ static void nested_svm_invalidate_vmcb02_insn_bytes(struct vcpu_svm *svm)
svm->nested.vmcb02_insn_bytes_valid = false;
}
+static void nested_svm_update_vmcb12_insn_bytes(struct kvm_vcpu *vcpu,
+ struct vmcb *vmcb12,
+ const struct vmcb *vmcb02)
+{
+ struct vcpu_svm *svm = to_svm(vcpu);
+
+ if (!guest_cpu_cap_has(vcpu, X86_FEATURE_DECODEASSISTS))
+ goto out;
+
+ if (!nested_svm_vmexit_supports_insn_bytes(vmcb02) ||
+ !svm->nested.vmcb02_insn_bytes_valid) {
+ nested_svm_invalidate_insn_bytes(vmcb12);
+ goto out;
+ }
+
+ nested_svm_copy_insn_bytes(vmcb12, vmcb02);
+
+out:
+ svm->nested.vmcb02_insn_bytes_valid = false;
+}
+
static void nested_svm_inject_npf_exit(struct kvm_vcpu *vcpu,
struct x86_exception *fault,
bool from_hardware)
@@ -1335,6 +1370,8 @@ static int nested_svm_vmexit_update_vmcb12(struct kvm_vcpu *vcpu)
if (guest_cpu_cap_has(vcpu, X86_FEATURE_NRIPS))
vmcb12->control.next_rip = vmcb02->control.next_rip;
+ nested_svm_update_vmcb12_insn_bytes(vcpu, vmcb12, vmcb02);
+
if (nested_vmcb12_has_lbrv(vcpu))
svm_copy_lbrs(&vmcb12->save, &vmcb02->save);
--
2.43.7
^ permalink raw reply [flat|nested] 11+ messages in thread* [PATCH v8 5/8] KVM: nSVM: Fetch DecodeAssist bytes for synthesized faults
2026-09-23 14:02 [PATCH v8 0/8] KVM: nSVM: Enable DecodeAssists for nested guests Tina Zhang
` (3 preceding siblings ...)
2026-09-23 14:02 ` [PATCH v8 4/8] KVM: nSVM: Propagate hardware DecodeAssist bytes to VMCB12 Tina Zhang
@ 2026-09-23 14:02 ` Tina Zhang
2026-09-23 22:20 ` Jim Mattson
2026-09-23 14:02 ` [PATCH v8 6/8] KVM: nSVM: Use emulator bytes for synthesized nested #NPF Tina Zhang
` (2 subsequent siblings)
7 siblings, 1 reply; 11+ messages in thread
From: Tina Zhang @ 2026-09-23 14:02 UTC (permalink / raw)
To: Sean Christopherson, Jim Mattson, kvm
Cc: Paolo Bonzini, Shuah Khan, zhouyanjing, linux-kselftest, linux-kernel
Hardware-reflected #NPF and #PF VM-Exits can propagate instruction bytes
from VMCB02, but KVM-synthesized exits have no hardware-provided state for
the current exit.
Extend kvm_read_guest_virt_helper() to optionally report the number of
bytes read, including partial reads. Add kvm_fetch_guest_virt() to apply
instruction-fetch permissions and return that count, reusing the generic
helper's page-by-page read loop.
When a synthesized data #NPF or #PF has no valid VMCB02 instruction bytes,
fetch up to 15 bytes from L2's RIP while constructing VMCB12. Preserve
the bytes already read if a subsequent read cannot be completed.
For instruction fetches, truncate each linear address to 32 bits outside
64-bit mode and stop at a non-canonical address in 64-bit mode. Limit
the fetch window at the code-segment limit outside 64-bit mode.
Do not attempt the fallback for SEV guests, as KVM cannot read encrypted
guest memory directly.
Signed-off-by: Tina Zhang <zhang_wei@open-hieco.net>
---
arch/x86/kvm/svm/nested.c | 41 +++++++++++++++++++++++++---
arch/x86/kvm/x86.c | 56 +++++++++++++++++++++++++++++++--------
arch/x86/kvm/x86.h | 2 ++
3 files changed, 85 insertions(+), 14 deletions(-)
diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index e839f61211c9..813b0fc663c6 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -78,22 +78,57 @@ static void nested_svm_invalidate_vmcb02_insn_bytes(struct vcpu_svm *svm)
svm->nested.vmcb02_insn_bytes_valid = false;
}
+static u8 nested_svm_get_insn_bytes_len(struct kvm_vcpu *vcpu, u8 max_bytes)
+{
+ if (!is_64_bit_mode(vcpu)) {
+ u32 eip = kvm_rip_read(vcpu);
+ u32 limit = to_svm(vcpu)->vmcb->save.cs.limit;
+
+ if (eip > limit)
+ return 0;
+ max_bytes = min_t(u64, max_bytes, (u64)limit - eip + 1);
+ }
+
+ return max_bytes;
+}
+
+static u8 nested_svm_fetch_insn_bytes(struct kvm_vcpu *vcpu, u8 *bytes,
+ u8 max_bytes)
+{
+ gva_t rip = kvm_get_linear_rip(vcpu);
+
+ max_bytes = nested_svm_get_insn_bytes_len(vcpu, max_bytes);
+
+ return kvm_fetch_guest_virt(vcpu, rip, bytes, max_bytes);
+}
+
static void nested_svm_update_vmcb12_insn_bytes(struct kvm_vcpu *vcpu,
struct vmcb *vmcb12,
const struct vmcb *vmcb02)
{
struct vcpu_svm *svm = to_svm(vcpu);
+ const u8 max_bytes = sizeof(vmcb12->control.insn_bytes);
if (!guest_cpu_cap_has(vcpu, X86_FEATURE_DECODEASSISTS))
goto out;
- if (!nested_svm_vmexit_supports_insn_bytes(vmcb02) ||
- !svm->nested.vmcb02_insn_bytes_valid) {
+ if (!nested_svm_vmexit_supports_insn_bytes(vmcb02)) {
nested_svm_invalidate_insn_bytes(vmcb12);
goto out;
}
- nested_svm_copy_insn_bytes(vmcb12, vmcb02);
+ if (svm->nested.vmcb02_insn_bytes_valid) {
+ nested_svm_copy_insn_bytes(vmcb12, vmcb02);
+ goto out;
+ }
+
+ if (!is_sev_guest(vcpu))
+ vmcb12->control.insn_len =
+ nested_svm_fetch_insn_bytes(vcpu,
+ vmcb12->control.insn_bytes,
+ max_bytes);
+ else
+ nested_svm_invalidate_insn_bytes(vmcb12);
out:
svm->nested.vmcb02_insn_bytes_valid = false;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 1705e7be46ec..ad8b35f2219d 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4772,20 +4772,34 @@ gpa_t kvm_mmu_gva_to_gpa_system(struct kvm_vcpu *vcpu, gva_t gva,
static int kvm_read_guest_virt_helper(gva_t addr, void *val, unsigned int bytes,
struct kvm_vcpu *vcpu, u64 access,
- struct x86_exception *exception)
+ struct x86_exception *exception,
+ unsigned int *bytes_read)
{
struct kvm_pagewalk *gva_walk = &vcpu->arch.gva_walk;
void *data = val;
int r = X86EMUL_CONTINUE;
while (bytes) {
- gpa_t gpa = gva_walk->gva_to_gpa(vcpu, gva_walk, addr, access, exception);
+ gpa_t gpa;
unsigned offset = addr & (PAGE_SIZE-1);
unsigned toread = min(bytes, (unsigned)PAGE_SIZE - offset);
int ret;
- if (gpa == INVALID_GPA)
- return X86EMUL_PROPAGATE_FAULT;
+ /* Apply address wrapping or canonicality checks before each fetch chunk. */
+ if (access & PFERR_FETCH_MASK) {
+ if (!is_64_bit_mode(vcpu))
+ addr = (u32)addr;
+ else if (is_noncanonical_address(addr, vcpu, 0)) {
+ r = X86EMUL_UNHANDLEABLE;
+ goto out;
+ }
+ }
+
+ gpa = gva_walk->gva_to_gpa(vcpu, gva_walk, addr, access, exception);
+ if (gpa == INVALID_GPA) {
+ r = X86EMUL_PROPAGATE_FAULT;
+ goto out;
+ }
ret = kvm_vcpu_read_guest_page(vcpu, gpa >> PAGE_SHIFT, data,
offset, toread);
if (ret < 0) {
@@ -4798,13 +4812,32 @@ static int kvm_read_guest_virt_helper(gva_t addr, void *val, unsigned int bytes,
addr += toread;
}
out:
+ if (bytes_read)
+ *bytes_read = data - val;
return r;
}
-/* used for instruction fetching */
-static int kvm_fetch_guest_virt(struct x86_emulate_ctxt *ctxt,
- gva_t addr, void *val, unsigned int bytes,
- struct x86_exception *exception)
+/* Return the number of instruction bytes read, including partial reads. */
+unsigned int kvm_fetch_guest_virt(struct kvm_vcpu *vcpu, gva_t addr,
+ void *val, unsigned int bytes)
+{
+ struct x86_exception exception = {};
+ unsigned int bytes_read;
+ u64 access = PFERR_FETCH_MASK;
+
+ if (kvm_x86_call(get_cpl)(vcpu) == 3)
+ access |= PFERR_USER_MASK;
+
+ kvm_read_guest_virt_helper(addr, val, bytes, vcpu, access,
+ &exception, &bytes_read);
+ return bytes_read;
+}
+EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_fetch_guest_virt);
+
+static int emulator_fetch_guest_virt(struct x86_emulate_ctxt *ctxt,
+ gva_t addr, void *val,
+ unsigned int bytes,
+ struct x86_exception *exception)
{
struct kvm_vcpu *vcpu = emul_to_vcpu(ctxt);
struct kvm_pagewalk *gva_walk = &vcpu->arch.gva_walk;
@@ -4843,7 +4876,7 @@ int kvm_read_guest_virt(struct kvm_vcpu *vcpu,
*/
memset(exception, 0, sizeof(*exception));
return kvm_read_guest_virt_helper(addr, val, bytes, vcpu, access,
- exception);
+ exception, NULL);
}
EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_read_guest_virt);
@@ -4859,7 +4892,8 @@ static int emulator_read_std(struct x86_emulate_ctxt *ctxt,
else if (kvm_x86_call(get_cpl)(vcpu) == 3)
access |= PFERR_USER_MASK;
- return kvm_read_guest_virt_helper(addr, val, bytes, vcpu, access, exception);
+ return kvm_read_guest_virt_helper(addr, val, bytes, vcpu, access,
+ exception, NULL);
}
static int kvm_write_guest_virt_helper(gva_t addr, void *val, unsigned int bytes,
@@ -5771,7 +5805,7 @@ static const struct x86_emulate_ops emulate_ops = {
.write_gpr = emulator_write_gpr,
.read_std = emulator_read_std,
.write_std = emulator_write_std,
- .fetch = kvm_fetch_guest_virt,
+ .fetch = emulator_fetch_guest_virt,
.read_emulated = emulator_read_emulated,
.write_emulated = emulator_write_emulated,
.cmpxchg_emulated = emulator_cmpxchg_emulated,
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index 1d9a66048b01..dbf0a4e6e9c1 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -357,6 +357,8 @@ static inline void adjust_tsc_offset_host(struct kvm_vcpu *vcpu, s64 adjustment)
int kvm_read_guest_virt(struct kvm_vcpu *vcpu,
gva_t addr, void *val, unsigned int bytes,
struct x86_exception *exception);
+unsigned int kvm_fetch_guest_virt(struct kvm_vcpu *vcpu, gva_t addr,
+ void *val, unsigned int bytes);
int kvm_write_guest_virt_system(struct kvm_vcpu *vcpu,
gva_t addr, void *val, unsigned int bytes,
--
2.43.7
^ permalink raw reply [flat|nested] 11+ messages in thread* Re: [PATCH v8 5/8] KVM: nSVM: Fetch DecodeAssist bytes for synthesized faults
2026-09-23 14:02 ` [PATCH v8 5/8] KVM: nSVM: Fetch DecodeAssist bytes for synthesized faults Tina Zhang
@ 2026-09-23 22:20 ` Jim Mattson
0 siblings, 0 replies; 11+ messages in thread
From: Jim Mattson @ 2026-09-23 22:20 UTC (permalink / raw)
To: Tina Zhang
Cc: Sean Christopherson, kvm, Paolo Bonzini, Shuah Khan, zhouyanjing,
linux-kselftest, linux-kernel
On Wed, Sep 23, 2026 at 7:03 AM Tina Zhang <zhang_wei@open-hieco.net> wrote:
>
> Hardware-reflected #NPF and #PF VM-Exits can propagate instruction bytes
> from VMCB02, but KVM-synthesized exits have no hardware-provided state for
> the current exit.
>
> Extend kvm_read_guest_virt_helper() to optionally report the number of
> bytes read, including partial reads. Add kvm_fetch_guest_virt() to apply
> instruction-fetch permissions and return that count, reusing the generic
> helper's page-by-page read loop.
>
> When a synthesized data #NPF or #PF has no valid VMCB02 instruction bytes,
> fetch up to 15 bytes from L2's RIP while constructing VMCB12. Preserve
> the bytes already read if a subsequent read cannot be completed.
>
> For instruction fetches, truncate each linear address to 32 bits outside
> 64-bit mode and stop at a non-canonical address in 64-bit mode. Limit
> the fetch window at the code-segment limit outside 64-bit mode.
>
> Do not attempt the fallback for SEV guests, as KVM cannot read encrypted
> guest memory directly.
>
> Signed-off-by: Tina Zhang <zhang_wei@open-hieco.net>
> ---
> arch/x86/kvm/svm/nested.c | 41 +++++++++++++++++++++++++---
> arch/x86/kvm/x86.c | 56 +++++++++++++++++++++++++++++++--------
> arch/x86/kvm/x86.h | 2 ++
> 3 files changed, 85 insertions(+), 14 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> index e839f61211c9..813b0fc663c6 100644
> --- a/arch/x86/kvm/svm/nested.c
> +++ b/arch/x86/kvm/svm/nested.c
> @@ -78,22 +78,57 @@ static void nested_svm_invalidate_vmcb02_insn_bytes(struct vcpu_svm *svm)
> svm->nested.vmcb02_insn_bytes_valid = false;
> }
>
> +static u8 nested_svm_get_insn_bytes_len(struct kvm_vcpu *vcpu, u8 max_bytes)
> +{
> + if (!is_64_bit_mode(vcpu)) {
> + u32 eip = kvm_rip_read(vcpu);
> + u32 limit = to_svm(vcpu)->vmcb->save.cs.limit;
> +
> + if (eip > limit)
> + return 0;
> + max_bytes = min_t(u64, max_bytes, (u64)limit - eip + 1);
> + }
> +
> + return max_bytes;
> +}
> +
> +static u8 nested_svm_fetch_insn_bytes(struct kvm_vcpu *vcpu, u8 *bytes,
> + u8 max_bytes)
> +{
> + gva_t rip = kvm_get_linear_rip(vcpu);
> +
> + max_bytes = nested_svm_get_insn_bytes_len(vcpu, max_bytes);
> +
> + return kvm_fetch_guest_virt(vcpu, rip, bytes, max_bytes);
> +}
> +
> static void nested_svm_update_vmcb12_insn_bytes(struct kvm_vcpu *vcpu,
> struct vmcb *vmcb12,
> const struct vmcb *vmcb02)
> {
> struct vcpu_svm *svm = to_svm(vcpu);
> + const u8 max_bytes = sizeof(vmcb12->control.insn_bytes);
>
> if (!guest_cpu_cap_has(vcpu, X86_FEATURE_DECODEASSISTS))
> goto out;
>
> - if (!nested_svm_vmexit_supports_insn_bytes(vmcb02) ||
> - !svm->nested.vmcb02_insn_bytes_valid) {
> + if (!nested_svm_vmexit_supports_insn_bytes(vmcb02)) {
> nested_svm_invalidate_insn_bytes(vmcb12);
> goto out;
> }
>
> - nested_svm_copy_insn_bytes(vmcb12, vmcb02);
> + if (svm->nested.vmcb02_insn_bytes_valid) {
> + nested_svm_copy_insn_bytes(vmcb12, vmcb02);
> + goto out;
> + }
> +
> + if (!is_sev_guest(vcpu))
> + vmcb12->control.insn_len =
> + nested_svm_fetch_insn_bytes(vcpu,
> + vmcb12->control.insn_bytes,
> + max_bytes);
> + else
> + nested_svm_invalidate_insn_bytes(vmcb12);
>
> out:
> svm->nested.vmcb02_insn_bytes_valid = false;
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 1705e7be46ec..ad8b35f2219d 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -4772,20 +4772,34 @@ gpa_t kvm_mmu_gva_to_gpa_system(struct kvm_vcpu *vcpu, gva_t gva,
>
> static int kvm_read_guest_virt_helper(gva_t addr, void *val, unsigned int bytes,
> struct kvm_vcpu *vcpu, u64 access,
> - struct x86_exception *exception)
> + struct x86_exception *exception,
> + unsigned int *bytes_read)
> {
> struct kvm_pagewalk *gva_walk = &vcpu->arch.gva_walk;
> void *data = val;
> int r = X86EMUL_CONTINUE;
>
> while (bytes) {
> - gpa_t gpa = gva_walk->gva_to_gpa(vcpu, gva_walk, addr, access, exception);
> + gpa_t gpa;
> unsigned offset = addr & (PAGE_SIZE-1);
> unsigned toread = min(bytes, (unsigned)PAGE_SIZE - offset);
> int ret;
>
> - if (gpa == INVALID_GPA)
> - return X86EMUL_PROPAGATE_FAULT;
> + /* Apply address wrapping or canonicality checks before each fetch chunk. */
> + if (access & PFERR_FETCH_MASK) {
> + if (!is_64_bit_mode(vcpu))
> + addr = (u32)addr;
> + else if (is_noncanonical_address(addr, vcpu, 0)) {
> + r = X86EMUL_UNHANDLEABLE;
> + goto out;
> + }
> + }
I hadn't anticipated the need for this special-case, and it's more
intrusive than just returning the number of bytes read.
I see now that it's complicated to match the behavior of the
emulator's __do_insn_fetch_bytes(). You could clamp the number of
bytes to read up-front to deal with the end of the address space, but
you would still need a second call to handle the wrap. Something like
the following (mangled by my MUA):
static unsigned int __kvm_fetch_guest_virt(struct kvm_vcpu *vcpu, gva_t addr,
void *val, unsigned int bytes)
{
struct x86_exception exception = {};
unsigned int bytes_read;
u64 access = PFERR_FETCH_MASK;
if (kvm_x86_call(get_cpl)(vcpu) == 3)
access |= PFERR_USER_MASK;
kvm_read_guest_virt_helper(addr, val, bytes, vcpu, access,
&exception, &bytes_read);
return bytes_read;
}
unsigned int kvm_fetch_guest_virt(struct kvm_vcpu *vcpu, gva_t addr,
void *val, unsigned int bytes)
{
unsigned int first, bytes_read;
bool wraps;
u64 avail;
/* An instruction-sized fetch can wrap at most once. */
if (WARN_ON_ONCE(bytes > X86_MAX_INSTRUCTION_LENGTH))
return 0;
if (!is_64_bit_mode(vcpu)) {
addr = (u32)addr;
avail = BIT_ULL(32) - addr;
wraps = true;
} else if (is_noncanonical_address(addr, vcpu, 0)) {
return 0;
} else if (addr < BIT_ULL(63)) {
avail = BIT_ULL(vcpu_virt_addr_bits(vcpu) - 1) - addr;
wraps = false;
} else {
avail = -addr;
wraps = true;
}
first = min_t(u64, bytes, avail);
bytes_read = __kvm_fetch_guest_virt(vcpu, addr, val, first);
if (wraps && bytes_read == first && first < bytes)
bytes_read += __kvm_fetch_guest_virt(vcpu, 0, val + first,
bytes - first);
return bytes_read;
}
I think this solution may be worse than what you have now, but I will
defer to Sean. Maybe he will have a better idea. (Maybe my suggestion
to return the number of bytes read was misguided.)
Reviewed-by: Jim Mattson <jmattson@google.com>
^ permalink raw reply [flat|nested] 11+ messages in thread
* [PATCH v8 6/8] KVM: nSVM: Use emulator bytes for synthesized nested #NPF
2026-09-23 14:02 [PATCH v8 0/8] KVM: nSVM: Enable DecodeAssists for nested guests Tina Zhang
` (4 preceding siblings ...)
2026-09-23 14:02 ` [PATCH v8 5/8] KVM: nSVM: Fetch DecodeAssist bytes for synthesized faults Tina Zhang
@ 2026-09-23 14:02 ` Tina Zhang
2026-09-23 14:02 ` [PATCH v8 7/8] KVM: nSVM: Advertise DecodeAssists to L1 Tina Zhang
2026-09-23 14:02 ` [PATCH v8 8/8] KVM: selftests: Add nested SVM DecodeAssists test Tina Zhang
7 siblings, 0 replies; 11+ messages in thread
From: Tina Zhang @ 2026-09-23 14:02 UTC (permalink / raw)
To: Sean Christopherson, Jim Mattson, kvm
Cc: Paolo Bonzini, Shuah Khan, zhouyanjing, linux-kselftest, linux-kernel
Preserve the bytes used by the emulator when synthesizing a data #NPF.
Reuse the fetch cache only when the fault is the current emulator
exception, identified by fault == &ctxt->exception.
Add an emulator accessor to copy cached instruction bytes, checking
the RIP and cache bounds. These checks alone do not establish that
the cache belongs to the current emulation.
Write the cached bytes directly to VMCB02 and fetch any missing tail
through the instruction-fetch helper. If the tail cannot be read,
report only the bytes already available. For SEV guests, retain only
the cached bytes because KVM cannot fetch plaintext guest instructions.
Signed-off-by: Tina Zhang <zhang_wei@open-hieco.net>
Reviewed-by: Jim Mattson <jmattson@google.com>
---
arch/x86/kvm/emulate.c | 22 ++++++++++++++++++++++
arch/x86/kvm/kvm_emulate.h | 3 +++
arch/x86/kvm/svm/nested.c | 36 ++++++++++++++++++++++++++++++++++--
3 files changed, 59 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 299aeaca6cf2..f15780116e8d 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -900,6 +900,28 @@ static __always_inline int do_insn_fetch_bytes(struct x86_emulate_ctxt *ctxt,
return X86EMUL_CONTINUE;
}
+/*
+ * The caller is responsible for ensuring that the fetch cache belongs to
+ * the current instruction. Matching EIP alone does not guarantee this.
+ */
+unsigned int x86_emulator_copy_insn_bytes(struct x86_emulate_ctxt *ctxt,
+ unsigned long eip, u8 *bytes,
+ unsigned int max_bytes)
+{
+ unsigned int nr_bytes;
+
+ if (!ctxt || ctxt->eip != eip ||
+ ctxt->fetch.end < ctxt->fetch.data ||
+ ctxt->fetch.end > ctxt->fetch.data + sizeof(ctxt->fetch.data))
+ return 0;
+
+ nr_bytes = min_t(unsigned int, ctxt->fetch.end - ctxt->fetch.data,
+ max_bytes);
+ memcpy(bytes, ctxt->fetch.data, nr_bytes);
+ return nr_bytes;
+}
+EXPORT_SYMBOL_FOR_KVM_INTERNAL(x86_emulator_copy_insn_bytes);
+
/* Fetch next part of the instruction being emulated. */
#define insn_fetch(_type, _ctxt) \
({ _type _x; \
diff --git a/arch/x86/kvm/kvm_emulate.h b/arch/x86/kvm/kvm_emulate.h
index d05558ef28ae..5361d42e6e05 100644
--- a/arch/x86/kvm/kvm_emulate.h
+++ b/arch/x86/kvm/kvm_emulate.h
@@ -528,6 +528,9 @@ enum x86_intercept {
};
int x86_decode_insn(struct x86_emulate_ctxt *ctxt, void *insn, int insn_len, int emulation_type);
+unsigned int x86_emulator_copy_insn_bytes(struct x86_emulate_ctxt *ctxt,
+ unsigned long eip, u8 *bytes,
+ unsigned int max_bytes);
bool x86_page_table_writing_insn(struct x86_emulate_ctxt *ctxt);
#define EMULATION_FAILED -1
#define EMULATION_OK 0
diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 813b0fc663c6..c1aef51bc1be 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -93,13 +93,40 @@ static u8 nested_svm_get_insn_bytes_len(struct kvm_vcpu *vcpu, u8 max_bytes)
}
static u8 nested_svm_fetch_insn_bytes(struct kvm_vcpu *vcpu, u8 *bytes,
- u8 max_bytes)
+ u8 count, u8 max_bytes)
{
gva_t rip = kvm_get_linear_rip(vcpu);
max_bytes = nested_svm_get_insn_bytes_len(vcpu, max_bytes);
+ count = min(count, max_bytes);
- return kvm_fetch_guest_virt(vcpu, rip, bytes, max_bytes);
+ return count + kvm_fetch_guest_virt(vcpu, rip + count, bytes + count,
+ max_bytes - count);
+}
+
+static void nested_svm_prepare_synthesized_insn_bytes(struct kvm_vcpu *vcpu)
+{
+ struct vcpu_svm *svm = to_svm(vcpu);
+ struct vmcb *vmcb02 = svm->nested.vmcb02.ptr;
+ struct x86_emulate_ctxt *ctxt = vcpu->arch.emulate_ctxt;
+ u8 max_bytes = sizeof(vmcb02->control.insn_bytes);
+ u8 count;
+
+ nested_svm_invalidate_vmcb02_insn_bytes(svm);
+
+ if (!guest_cpu_cap_has(vcpu, X86_FEATURE_DECODEASSISTS))
+ return;
+
+ max_bytes = nested_svm_get_insn_bytes_len(vcpu, max_bytes);
+ count = x86_emulator_copy_insn_bytes(ctxt, kvm_rip_read(vcpu),
+ vmcb02->control.insn_bytes, max_bytes);
+ if (!is_sev_guest(vcpu))
+ count = nested_svm_fetch_insn_bytes(vcpu,
+ vmcb02->control.insn_bytes,
+ count, max_bytes);
+ vmcb02->control.insn_len = count;
+
+ svm->nested.vmcb02_insn_bytes_valid = true;
}
static void nested_svm_update_vmcb12_insn_bytes(struct kvm_vcpu *vcpu,
@@ -126,6 +153,7 @@ static void nested_svm_update_vmcb12_insn_bytes(struct kvm_vcpu *vcpu,
vmcb12->control.insn_len =
nested_svm_fetch_insn_bytes(vcpu,
vmcb12->control.insn_bytes,
+ 0,
max_bytes);
else
nested_svm_invalidate_insn_bytes(vmcb12);
@@ -140,6 +168,8 @@ static void nested_svm_inject_npf_exit(struct kvm_vcpu *vcpu,
{
struct vcpu_svm *svm = to_svm(vcpu);
struct vmcb *vmcb = svm->vmcb;
+ struct x86_emulate_ctxt *ctxt = vcpu->arch.emulate_ctxt;
+ bool from_emulation = ctxt && fault == &ctxt->exception;
u64 fault_stage;
/*
@@ -169,6 +199,8 @@ static void nested_svm_inject_npf_exit(struct kvm_vcpu *vcpu,
if (from_hardware)
nested_svm_set_vmcb02_insn_bytes_valid(svm);
+ else if (from_emulation && !(fault->error_code & PFERR_FETCH_MASK))
+ nested_svm_prepare_synthesized_insn_bytes(vcpu);
else
nested_svm_invalidate_vmcb02_insn_bytes(svm);
nested_svm_vmexit(svm);
--
2.43.7
^ permalink raw reply [flat|nested] 11+ messages in thread* [PATCH v8 7/8] KVM: nSVM: Advertise DecodeAssists to L1
2026-09-23 14:02 [PATCH v8 0/8] KVM: nSVM: Enable DecodeAssists for nested guests Tina Zhang
` (5 preceding siblings ...)
2026-09-23 14:02 ` [PATCH v8 6/8] KVM: nSVM: Use emulator bytes for synthesized nested #NPF Tina Zhang
@ 2026-09-23 14:02 ` Tina Zhang
2026-09-23 14:02 ` [PATCH v8 8/8] KVM: selftests: Add nested SVM DecodeAssists test Tina Zhang
7 siblings, 0 replies; 11+ messages in thread
From: Tina Zhang @ 2026-09-23 14:02 UTC (permalink / raw)
To: Sean Christopherson, Jim Mattson, kvm
Cc: Paolo Bonzini, Shuah Khan, zhouyanjing, linux-kselftest, linux-kernel
Advertise DecodeAssists to L1 now that KVM virtualizes the
guest-visible DecodeAssist state in VMCB12: EXITINFO1 decode data for
MOV CR/DR, INTn, and INVLPG exits, plus instruction bytes for nested
page faults and intercepted #PF exits. INVLPGA's linear address remains
available directly from the saved guest rAX, as required by the APM.
Expose the feature only when supported by hardware, as KVM still relies
on hardware DecodeAssists for VM-Exits that are reflected directly from
L2.
With DecodeAssists exposed, QEMU configurations that require the feature
(e.g. "-cpu ...,+decodeassists,...,enforce") are no longer rejected.
Signed-off-by: Tina Zhang <zhang_wei@open-hieco.net>
Reviewed-by: Jim Mattson <jmattson@google.com>
---
arch/x86/kvm/cpuid.c | 1 +
arch/x86/kvm/svm/svm.c | 2 ++
2 files changed, 3 insertions(+)
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 7c63ef90fc60..52dcde011987 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -1195,6 +1195,7 @@ void kvm_initialize_cpu_caps(void)
VENDOR_F(NPT),
VENDOR_F(VMCBCLEAN),
VENDOR_F(FLUSHBYASID),
+ VENDOR_F(DECODEASSISTS),
VENDOR_F(NRIPS),
VENDOR_F(TSCRATEMSR),
VENDOR_F(V_VMSAVE_VMLOAD),
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index e83e4e5e7b93..82de844f63ad 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -5557,6 +5557,8 @@ static __init void svm_set_cpu_caps(void)
*/
kvm_cpu_cap_set(X86_FEATURE_FLUSHBYASID);
+ kvm_cpu_cap_check_and_set(X86_FEATURE_DECODEASSISTS);
+
if (nrips)
kvm_cpu_cap_set(X86_FEATURE_NRIPS);
--
2.43.7
^ permalink raw reply [flat|nested] 11+ messages in thread* [PATCH v8 8/8] KVM: selftests: Add nested SVM DecodeAssists test
2026-09-23 14:02 [PATCH v8 0/8] KVM: nSVM: Enable DecodeAssists for nested guests Tina Zhang
` (6 preceding siblings ...)
2026-09-23 14:02 ` [PATCH v8 7/8] KVM: nSVM: Advertise DecodeAssists to L1 Tina Zhang
@ 2026-09-23 14:02 ` Tina Zhang
7 siblings, 0 replies; 11+ messages in thread
From: Tina Zhang @ 2026-09-23 14:02 UTC (permalink / raw)
To: Sean Christopherson, Jim Mattson, kvm
Cc: Paolo Bonzini, Shuah Khan, zhouyanjing, linux-kselftest, linux-kernel
Add a focused nested SVM selftest for DecodeAssists. Verify that KVM
exposes the feature to L1 and provides EXITINFO for representative
MOV CR/DR, CLTS, INTn, INVLPG, and INVLPGA intercepts, including a
MOV-to-CR0 selective intercept. Check hardware and forced-emulation
paths against the same expected values. Poison the instruction-byte
fields before each instruction-intercept test and verify that the byte
count is cleared on exit.
Exercise instruction bytes for hardware and synthesized #NPF/#PF exits.
Cover a synthesized #NPF that follows a hardware #NPF in the same emulated
instruction, an unreadable instruction tail that leaves only the cached
opcode, and the absence of bytes for an instruction-fetch #PF. Modify the
MOVSB opcode while its MMIO read is pending to verify that the emulator's
cached bytes are preserved.
Inject a userspace #PF while an MMIO read is pending. Verify that after
MMIO completion, L1 receives instruction bytes from the current RIP,
not the previous instruction's emulator cache.
The hardware instruction-intercept, synthesized OUTSB #NPF, and
userspace-injected #PF cases run by default. The forced-emulation #PF
and instruction-intercept paths require kvm.force_emulation_prefix=1.
Signed-off-by: Tina Zhang <zhang_wei@open-hieco.net>
Reviewed-by: Jim Mattson <jmattson@google.com>
---
tools/testing/selftests/kvm/Makefile.kvm | 1 +
.../selftests/kvm/include/x86/processor.h | 1 +
.../kvm/x86/svm_nested_decode_assists_test.c | 590 ++++++++++++++++++
3 files changed, 592 insertions(+)
create mode 100644 tools/testing/selftests/kvm/x86/svm_nested_decode_assists_test.c
diff --git a/tools/testing/selftests/kvm/Makefile.kvm b/tools/testing/selftests/kvm/Makefile.kvm
index 239bc61ea384..de9423693399 100644
--- a/tools/testing/selftests/kvm/Makefile.kvm
+++ b/tools/testing/selftests/kvm/Makefile.kvm
@@ -118,6 +118,7 @@ TEST_GEN_PROGS_x86 += x86/vmx_preemption_timer_test
TEST_GEN_PROGS_x86 += x86/svm_vmcall_test
TEST_GEN_PROGS_x86 += x86/svm_int_ctl_test
TEST_GEN_PROGS_x86 += x86/svm_nested_clear_efer_svme
+TEST_GEN_PROGS_x86 += x86/svm_nested_decode_assists_test
TEST_GEN_PROGS_x86 += x86/svm_nested_shutdown_test
TEST_GEN_PROGS_x86 += x86/svm_nested_soft_inject_test
TEST_GEN_PROGS_x86 += x86/svm_nested_vmcb12_gpa
diff --git a/tools/testing/selftests/kvm/include/x86/processor.h b/tools/testing/selftests/kvm/include/x86/processor.h
index 7579e692bc2b..bd281f521eb1 100644
--- a/tools/testing/selftests/kvm/include/x86/processor.h
+++ b/tools/testing/selftests/kvm/include/x86/processor.h
@@ -222,6 +222,7 @@ struct kvm_x86_cpu_feature {
#define X86_FEATURE_LBRV KVM_X86_CPU_FEATURE(0x8000000A, 0, EDX, 1)
#define X86_FEATURE_NRIPS KVM_X86_CPU_FEATURE(0x8000000A, 0, EDX, 3)
#define X86_FEATURE_TSCRATEMSR KVM_X86_CPU_FEATURE(0x8000000A, 0, EDX, 4)
+#define X86_FEATURE_DECODEASSISTS KVM_X86_CPU_FEATURE(0x8000000A, 0, EDX, 7)
#define X86_FEATURE_PAUSEFILTER KVM_X86_CPU_FEATURE(0x8000000A, 0, EDX, 10)
#define X86_FEATURE_PFTHRESHOLD KVM_X86_CPU_FEATURE(0x8000000A, 0, EDX, 12)
#define X86_FEATURE_V_VMSAVE_VMLOAD KVM_X86_CPU_FEATURE(0x8000000A, 0, EDX, 15)
diff --git a/tools/testing/selftests/kvm/x86/svm_nested_decode_assists_test.c b/tools/testing/selftests/kvm/x86/svm_nested_decode_assists_test.c
new file mode 100644
index 000000000000..aba91d8bb1a2
--- /dev/null
+++ b/tools/testing/selftests/kvm/x86/svm_nested_decode_assists_test.c
@@ -0,0 +1,590 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Test KVM's virtualization of SVM DecodeAssists for nested guests.
+ */
+
+#include "test_util.h"
+#include "kvm_util.h"
+#include "processor.h"
+#include "svm_util.h"
+
+#define TEST_INT_VECTOR 0x81
+
+/* Any canonical virtual address that is never mapped by the selftest VM. */
+#define PF_TEST_GVA BIT_ULL(40)
+#define PF_FETCH_TEST_GVA BIT_ULL(41)
+
+#define OUTSB_OPCODE 0x6e
+#define MOVSB_OPCODE 0xa4
+#define NOP_OPCODE 0x90
+#define BOUNDARY_OUTSB_CODE_SIZE 15
+#define TEST_IOPM_SIZE (3 * PAGE_SIZE)
+
+static u8 npf_target[PAGE_SIZE] __aligned(PAGE_SIZE);
+static u8 mmio_source[PAGE_SIZE] __aligned(PAGE_SIZE);
+static u8 boundary_outsb_code[2 * PAGE_SIZE] __aligned(PAGE_SIZE);
+
+static void l2_read_code(void)
+{
+ asm volatile("mov (%0), %%rax" : : "r"(&npf_target) : "rax", "memory");
+ GUEST_FAIL("L2 read did not cause a nested page fault");
+}
+
+static void l2_outsb_code(void)
+{
+ asm volatile("mov %0, %%rsi\n\t"
+ "mov $0x80, %%dx\n\t"
+ "outsb"
+ : : "r"(&npf_target) : "rsi", "rdx", "memory");
+ GUEST_FAIL("L2 OUTSB did not cause a nested page fault");
+}
+
+extern u8 l2_movsb_insn[];
+
+static void l2_movsb_code(void)
+{
+ asm volatile("mov %0, %%rsi\n\t"
+ "mov %1, %%rdi\n\t"
+ "l2_movsb_insn:\n\t"
+ "movsb"
+ : : "r"(&mmio_source), "r"(&npf_target)
+ : "rsi", "rdi", "memory");
+ GUEST_FAIL("L2 MOVSB did not cause a nested page fault");
+}
+
+extern u8 l2_userspace_pf_insn[];
+
+static void l2_userspace_pf_code(void)
+{
+ asm volatile("movzbl (%0), %%eax\n\t"
+ "l2_userspace_pf_insn:\n\t"
+ "nop"
+ : : "r"(&mmio_source) : "rax", "memory");
+ GUEST_FAIL("Userspace-injected #PF was not intercepted by L1");
+}
+
+static void l2_pf_code(void)
+{
+ asm volatile("mov (%0), %%rax"
+ : : "r"(PF_TEST_GVA) : "rax", "memory");
+ GUEST_FAIL("L2 access to an unmapped VA did not #PF");
+}
+
+static void l2_fep_pf_code(void)
+{
+ asm volatile(KVM_FEP "mov (%0), %%rax"
+ : : "r"(PF_TEST_GVA) : "rax", "memory");
+ GUEST_FAIL("L2 forced-emulated access to an unmapped VA did not #PF");
+}
+
+static void l2_mov_from_cr4_code(bool fep)
+{
+ if (fep)
+ asm volatile(KVM_FEP "mov %%cr4, %%r10" : : : "r10");
+ else
+ asm volatile("mov %%cr4, %%r10" : : : "r10");
+ GUEST_FAIL("L2 MOV-from-CR4 was not intercepted");
+}
+
+static void l2_mov_to_cr0_code(bool fep)
+{
+ u64 cr0;
+
+ asm volatile("mov %%cr0, %0" : "=r"(cr0));
+ cr0 ^= X86_CR0_WP;
+ if (fep)
+ asm volatile(KVM_FEP "mov %0, %%cr0" : : "a"(cr0) : "memory");
+ else
+ asm volatile("mov %0, %%cr0" : : "a"(cr0) : "memory");
+ GUEST_FAIL("L2 MOV-to-CR0 was not intercepted");
+}
+
+static void l2_mov_to_dr7_code(bool fep)
+{
+ u64 dr7;
+
+ asm volatile("mov %%dr7, %0" : "=r"(dr7));
+ if (fep)
+ asm volatile(KVM_FEP "mov %0, %%dr7" : : "b"(dr7));
+ else
+ asm volatile("mov %0, %%dr7" : : "b"(dr7));
+ GUEST_FAIL("L2 MOV-to-DR7 was not intercepted");
+}
+
+static void l2_clts_code(bool fep)
+{
+ if (fep)
+ asm volatile(KVM_FEP "clts" : : : "memory");
+ else
+ asm volatile("clts" : : : "memory");
+ GUEST_FAIL("L2 CLTS was not intercepted");
+}
+
+static void l2_int_code(bool fep)
+{
+ if (fep)
+ asm volatile(KVM_FEP "int %0" : : "i"(TEST_INT_VECTOR));
+ else
+ asm volatile("int %0" : : "i"(TEST_INT_VECTOR));
+ GUEST_FAIL("L2 INTn was not intercepted");
+}
+
+static void l2_invlpg_code(bool fep)
+{
+ if (fep)
+ asm volatile(KVM_FEP "invlpg (%0)" : : "r"(&npf_target) : "memory");
+ else
+ asm volatile("invlpg (%0)" : : "r"(&npf_target) : "memory");
+ GUEST_FAIL("L2 INVLPG was not intercepted");
+}
+
+static void l2_invlpga_code(bool fep)
+{
+ if (fep)
+ asm volatile(KVM_FEP "invlpga"
+ : : "a"(&npf_target), "c"(0) : "memory");
+ else
+ asm volatile("invlpga" : : "a"(&npf_target), "c"(0) : "memory");
+ GUEST_FAIL("L2 INVLPGA was not intercepted");
+}
+
+struct instruction_intercept_test {
+ const char *name;
+ void (*code)(bool fep);
+ u64 intercept;
+ u32 intercept_cr;
+ u32 intercept_dr;
+ u64 exit_code;
+ u64 exit_info_1;
+ u64 exit_info_1_mask;
+ bool check_rax;
+ u64 rax;
+};
+
+static const struct instruction_intercept_test instruction_intercept_tests[] = {
+ {
+ .name = "MOV-from-CR4",
+ .code = l2_mov_from_cr4_code,
+ .intercept_cr = BIT(INTERCEPT_CR4_READ),
+ .exit_code = SVM_EXIT_READ_CR4,
+ .exit_info_1 = BIT_ULL(63) | 10,
+ .exit_info_1_mask = ~0ULL,
+ }, {
+ .name = "MOV-to-CR0-selective",
+ .code = l2_mov_to_cr0_code,
+ .intercept = BIT_ULL(INTERCEPT_SELECTIVE_CR0),
+ .exit_code = SVM_EXIT_CR0_SEL_WRITE,
+ .exit_info_1 = BIT_ULL(63),
+ .exit_info_1_mask = ~0ULL,
+ }, {
+ .name = "MOV-to-DR7",
+ .code = l2_mov_to_dr7_code,
+ .intercept_dr = BIT(INTERCEPT_DR7_WRITE),
+ .exit_code = SVM_EXIT_WRITE_DR7,
+ .exit_info_1 = 3,
+ .exit_info_1_mask = ~0ULL,
+ }, {
+ .name = "CLTS",
+ .code = l2_clts_code,
+ .intercept_cr = BIT(INTERCEPT_CR0_WRITE),
+ .exit_code = SVM_EXIT_WRITE_CR0,
+ .exit_info_1_mask = BIT_ULL(63),
+ }, {
+ .name = "INTn",
+ .code = l2_int_code,
+ .intercept = BIT_ULL(INTERCEPT_INTn),
+ .exit_code = SVM_EXIT_SWINT,
+ .exit_info_1 = TEST_INT_VECTOR,
+ .exit_info_1_mask = ~0ULL,
+ }, {
+ .name = "INVLPG",
+ .code = l2_invlpg_code,
+ .intercept = BIT_ULL(INTERCEPT_INVLPG),
+ .exit_code = SVM_EXIT_INVLPG,
+ .exit_info_1 = (u64)&npf_target,
+ .exit_info_1_mask = ~0ULL,
+ }, {
+ .name = "INVLPGA",
+ .code = l2_invlpga_code,
+ .intercept = BIT_ULL(INTERCEPT_INVLPGA),
+ .exit_code = SVM_EXIT_INVLPGA,
+ .exit_info_1_mask = ~0ULL,
+ .check_rax = true,
+ .rax = (u64)&npf_target,
+ },
+};
+
+static void assert_decode_assist_insn_bytes(struct vmcb *vmcb)
+{
+ GUEST_ASSERT(vmcb->control.insn_len);
+ GUEST_ASSERT(vmcb->control.insn_len <=
+ sizeof(vmcb->control.insn_bytes));
+ GUEST_ASSERT(!memcmp(vmcb->control.insn_bytes,
+ (void *)vmcb->save.rip,
+ vmcb->control.insn_len));
+}
+
+static void assert_full_decode_assist_insn_bytes(struct vmcb *vmcb)
+{
+ GUEST_ASSERT_EQ(vmcb->control.insn_len,
+ sizeof(vmcb->control.insn_bytes));
+ assert_decode_assist_insn_bytes(vmcb);
+}
+
+static void prepare_l2_for_vmrun(struct svm_test_data *svm, gva_t rip)
+{
+ struct vmcb *vmcb = svm->vmcb;
+
+ vmcb->save.rip = rip;
+ vmcb->save.rsp = (u64)svm->stack;
+}
+
+static void run_intercept_test(struct svm_test_data *svm,
+ const struct instruction_intercept_test *test, bool fep)
+{
+ struct vmcb *vmcb = svm->vmcb;
+ struct vmcb_control_area *control = &vmcb->control;
+ u64 expected_exit_info_1 = test->exit_info_1 & test->exit_info_1_mask;
+ const char *mode = fep ? "emulated" : "hardware";
+
+ control->intercept |= test->intercept;
+ control->intercept_cr |= test->intercept_cr;
+ control->intercept_dr |= test->intercept_dr;
+
+ control->exit_info_1 = ~0ULL;
+ control->insn_len = sizeof(control->insn_bytes);
+ memset(control->insn_bytes, 0xa5, sizeof(control->insn_bytes));
+ prepare_l2_for_vmrun(svm, (u64)test->code);
+ guest_regs.rdi = fep;
+
+ run_guest(vmcb, svm->vmcb_gpa);
+
+ __GUEST_ASSERT(control->exit_code == test->exit_code,
+ "%s (%s): expected exit code %#lx, got %#lx",
+ test->name, mode, (unsigned long)test->exit_code,
+ (unsigned long)control->exit_code);
+ __GUEST_ASSERT((control->exit_info_1 & test->exit_info_1_mask) ==
+ expected_exit_info_1,
+ "%s (%s): expected EXITINFO1 %#lx with mask %#lx, got %#lx",
+ test->name, mode, (unsigned long)expected_exit_info_1,
+ (unsigned long)test->exit_info_1_mask,
+ (unsigned long)control->exit_info_1);
+ __GUEST_ASSERT(!control->insn_len,
+ "%s (%s): expected no instruction bytes, got %u",
+ test->name, mode, control->insn_len);
+
+ if (test->check_rax)
+ __GUEST_ASSERT(vmcb->save.rax == test->rax,
+ "%s (%s): expected rAX %#lx, got %#lx",
+ test->name, mode, (unsigned long)test->rax,
+ (unsigned long)vmcb->save.rax);
+
+ control->intercept &= ~test->intercept;
+ control->intercept_cr &= ~test->intercept_cr;
+ control->intercept_dr &= ~test->intercept_dr;
+}
+
+static void test_instruction_intercepts(struct svm_test_data *svm)
+{
+ int i;
+
+ for (i = 0; i < ARRAY_SIZE(instruction_intercept_tests); i++) {
+ run_intercept_test(svm, &instruction_intercept_tests[i], false);
+ if (is_forced_emulation_enabled)
+ run_intercept_test(svm, &instruction_intercept_tests[i], true);
+ }
+}
+
+static void test_hardware_npf(struct svm_test_data *svm, gpa_t npf_gpa)
+{
+ struct vmcb *vmcb = svm->vmcb;
+
+ prepare_l2_for_vmrun(svm, (u64)l2_read_code);
+ run_guest(vmcb, svm->vmcb_gpa);
+ GUEST_ASSERT_EQ(vmcb->control.exit_code, SVM_EXIT_NPF);
+ GUEST_ASSERT_EQ(vmcb->control.exit_info_2, npf_gpa);
+ assert_decode_assist_insn_bytes(vmcb);
+}
+
+/*
+ * The IOIO intercept causes L0 to emulate OUTSB before accessing its source
+ * operand. The emulated read then faults on L1's NPT, resulting in a
+ * KVM-synthesized #NPF.
+ */
+static void test_synthesized_npf(struct svm_test_data *svm, gpa_t npf_gpa)
+{
+ struct vmcb *vmcb = svm->vmcb;
+
+ prepare_l2_for_vmrun(svm, (u64)l2_outsb_code);
+ run_guest(vmcb, svm->vmcb_gpa);
+ GUEST_ASSERT_EQ(vmcb->control.exit_code, SVM_EXIT_NPF);
+ GUEST_ASSERT_EQ(vmcb->control.exit_info_2, npf_gpa);
+ assert_full_decode_assist_insn_bytes(vmcb);
+}
+
+/*
+ * MOVSB first reads from MMIO, causing a hardware #NPF that L0 emulates.
+ * After userspace completes the read, the emulated destination write faults
+ * on L1's NPT. The new #NPF must not reuse the original hardware exit's GPA.
+ * Userspace replaces MOVSB with NOP while the read is pending. DecodeAssist
+ * must retain the cached MOVSB bytes instead of re-reading the opcode.
+ */
+static void test_synthesized_npf_after_hardware_npf(struct svm_test_data *svm,
+ gpa_t npf_gpa)
+{
+ struct vmcb *vmcb = svm->vmcb;
+ u8 insn_bytes[sizeof(vmcb->control.insn_bytes)];
+
+ memcpy(insn_bytes, l2_movsb_insn, sizeof(insn_bytes));
+ GUEST_ASSERT_EQ(insn_bytes[0], MOVSB_OPCODE);
+ prepare_l2_for_vmrun(svm, (u64)l2_movsb_code);
+ run_guest(vmcb, svm->vmcb_gpa);
+ GUEST_ASSERT_EQ(vmcb->control.exit_code, SVM_EXIT_NPF);
+ GUEST_ASSERT_EQ(vmcb->control.exit_info_2, npf_gpa);
+ GUEST_ASSERT_EQ(vmcb->save.rip, (u64)l2_movsb_insn);
+ GUEST_ASSERT_EQ(l2_movsb_insn[0], NOP_OPCODE);
+ GUEST_ASSERT_EQ(vmcb->control.insn_len, sizeof(insn_bytes));
+ GUEST_ASSERT(!memcmp(vmcb->control.insn_bytes, insn_bytes,
+ sizeof(insn_bytes)));
+}
+
+/*
+ * OUTSB is the final byte of a mapped code page, and the following page is
+ * not present in L2's page tables. DecodeAssist byte fetching must stop at
+ * the page boundary and report only the OUTSB opcode.
+ */
+static void test_synthesized_npf_truncated(struct svm_test_data *svm,
+ gpa_t npf_gpa)
+{
+ struct vmcb *vmcb = svm->vmcb;
+
+ prepare_l2_for_vmrun(svm,
+ (u64)&boundary_outsb_code[PAGE_SIZE -
+ BOUNDARY_OUTSB_CODE_SIZE]);
+ run_guest(vmcb, svm->vmcb_gpa);
+ GUEST_ASSERT_EQ(vmcb->control.exit_code, SVM_EXIT_NPF);
+ GUEST_ASSERT_EQ(vmcb->control.exit_info_2, npf_gpa);
+ GUEST_ASSERT_EQ(vmcb->save.rip,
+ (u64)&boundary_outsb_code[PAGE_SIZE - 1]);
+ GUEST_ASSERT_EQ(vmcb->control.insn_len, 1);
+ GUEST_ASSERT_EQ(vmcb->control.insn_bytes[0], OUTSB_OPCODE);
+}
+
+static void test_hardware_intercepted_pf(struct svm_test_data *svm)
+{
+ struct vmcb *vmcb = svm->vmcb;
+
+ prepare_l2_for_vmrun(svm, (u64)l2_pf_code);
+ run_guest(vmcb, svm->vmcb_gpa);
+ GUEST_ASSERT_EQ(vmcb->control.exit_code, SVM_EXIT_EXCP_BASE + PF_VECTOR);
+ GUEST_ASSERT_EQ(vmcb->control.exit_info_2, PF_TEST_GVA);
+ GUEST_ASSERT(!(vmcb->control.exit_info_1 & PFERR_PRESENT_MASK));
+ GUEST_ASSERT(!(vmcb->control.exit_info_1 & PFERR_FETCH_MASK));
+ assert_decode_assist_insn_bytes(vmcb);
+}
+
+static void test_hardware_intercepted_fetch_pf(struct svm_test_data *svm)
+{
+ struct vmcb *vmcb = svm->vmcb;
+
+ prepare_l2_for_vmrun(svm, PF_FETCH_TEST_GVA);
+ run_guest(vmcb, svm->vmcb_gpa);
+ GUEST_ASSERT_EQ(vmcb->control.exit_code, SVM_EXIT_EXCP_BASE + PF_VECTOR);
+ GUEST_ASSERT_EQ(vmcb->control.exit_info_2, PF_FETCH_TEST_GVA);
+ GUEST_ASSERT(!(vmcb->control.exit_info_1 & PFERR_PRESENT_MASK));
+ GUEST_ASSERT(vmcb->control.exit_info_1 & PFERR_FETCH_MASK);
+ GUEST_ASSERT_EQ(vmcb->control.insn_len, 0);
+}
+
+static void test_synthesized_pf(struct svm_test_data *svm)
+{
+ struct vmcb *vmcb = svm->vmcb;
+
+ if (!is_forced_emulation_enabled)
+ return;
+
+ prepare_l2_for_vmrun(svm, (u64)l2_fep_pf_code);
+ run_guest(vmcb, svm->vmcb_gpa);
+ GUEST_ASSERT_EQ(vmcb->control.exit_code, SVM_EXIT_EXCP_BASE + PF_VECTOR);
+ GUEST_ASSERT_EQ(vmcb->control.exit_info_2, PF_TEST_GVA);
+ GUEST_ASSERT(!(vmcb->control.exit_info_1 & PFERR_PRESENT_MASK));
+ GUEST_ASSERT(!(vmcb->control.exit_info_1 & PFERR_FETCH_MASK));
+ assert_full_decode_assist_insn_bytes(vmcb);
+}
+
+/* The pending MMIO instruction must complete before reflecting userspace #PF. */
+static void test_userspace_injected_pf_during_emulation(struct svm_test_data *svm)
+{
+ struct vmcb *vmcb = svm->vmcb;
+
+ prepare_l2_for_vmrun(svm, (u64)l2_userspace_pf_code);
+ run_guest(vmcb, svm->vmcb_gpa);
+ GUEST_ASSERT_EQ(vmcb->control.exit_code, SVM_EXIT_EXCP_BASE + PF_VECTOR);
+ GUEST_ASSERT_EQ(vmcb->control.exit_info_1, 0);
+ GUEST_ASSERT_EQ(vmcb->control.exit_info_2, PF_TEST_GVA);
+ GUEST_ASSERT_EQ(vmcb->save.rip, (u64)l2_userspace_pf_insn);
+ GUEST_ASSERT_EQ(vmcb->save.rax, 0x5a);
+ assert_full_decode_assist_insn_bytes(vmcb);
+ GUEST_ASSERT_EQ(vmcb->control.insn_bytes[0], NOP_OPCODE);
+}
+
+static void l1_guest_code(struct svm_test_data *svm, gpa_t npf_gpa,
+ gpa_t iopm_gpa)
+{
+ struct vmcb *vmcb = svm->vmcb;
+
+ GUEST_ASSERT(this_cpu_has(X86_FEATURE_DECODEASSISTS));
+
+ generic_svm_setup(svm, l2_read_code);
+ vmcb->control.iopm_base_pa = iopm_gpa;
+
+ vmcb->control.intercept |= BIT_ULL(INTERCEPT_IOIO_PROT);
+ vmcb->control.intercept_exceptions |= 1U << PF_VECTOR;
+
+ test_hardware_npf(svm, npf_gpa);
+ test_synthesized_npf(svm, npf_gpa);
+ test_synthesized_npf_after_hardware_npf(svm, npf_gpa);
+ test_synthesized_npf_truncated(svm, npf_gpa);
+ test_hardware_intercepted_pf(svm);
+ test_hardware_intercepted_fetch_pf(svm);
+ test_synthesized_pf(svm);
+ test_userspace_injected_pf_during_emulation(svm);
+ test_instruction_intercepts(svm);
+
+ GUEST_DONE();
+}
+
+static void build_boundary_outsb_code(u8 *code)
+{
+ u64 source = (u64)&npf_target;
+
+ /* movabs $npf_target, %rsi */
+ code[0] = 0x48;
+ code[1] = 0xbe;
+ memcpy(&code[2], &source, sizeof(source));
+
+ /* mov $0x80, %dx; outsb */
+ code[10] = 0x66;
+ code[11] = 0xba;
+ code[12] = 0x80;
+ code[13] = 0x00;
+ code[14] = OUTSB_OPCODE;
+}
+
+static void prepare_boundary_outsb_code(struct kvm_vm *vm)
+{
+ gva_t code_gva = (gva_t)&boundary_outsb_code[PAGE_SIZE -
+ BOUNDARY_OUTSB_CODE_SIZE];
+
+ build_boundary_outsb_code(addr_gva2hva(vm, code_gva));
+}
+
+static void queue_userspace_pf(struct kvm_vcpu *vcpu)
+{
+ struct kvm_vcpu_events events;
+
+ vcpu_events_get(vcpu, &events);
+ TEST_ASSERT(!events.exception.pending && !events.exception.injected,
+ "Unexpected exception before userspace #PF injection");
+ TEST_ASSERT(events.flags & KVM_VCPUEVENT_VALID_PAYLOAD,
+ "KVM_CAP_EXCEPTION_PAYLOAD was not enabled");
+
+ events.exception.pending = true;
+ events.exception.nr = PF_VECTOR;
+ events.exception.has_error_code = true;
+ events.exception.error_code = 0;
+ events.exception_has_payload = true;
+ events.exception_payload = PF_TEST_GVA;
+ vcpu_events_set(vcpu, &events);
+}
+
+static void complete_mmio_read(struct kvm_vcpu *vcpu, gpa_t expected_gpa,
+ u8 value)
+{
+ if (vcpu->run->exit_reason == KVM_EXIT_IO) {
+ struct ucall uc;
+
+ if (get_ucall(vcpu, &uc) == UCALL_ABORT)
+ REPORT_GUEST_ASSERT(uc);
+ }
+
+ TEST_ASSERT_KVM_EXIT_REASON(vcpu, KVM_EXIT_MMIO);
+ TEST_ASSERT(!vcpu->run->mmio.is_write,
+ "Expected an MMIO read, got a write");
+ TEST_ASSERT_EQ(vcpu->run->mmio.phys_addr, expected_gpa);
+ TEST_ASSERT_EQ(vcpu->run->mmio.len, 1);
+ vcpu->run->mmio.data[0] = value;
+}
+
+static void assert_ucall_done(struct kvm_vcpu *vcpu)
+{
+ struct ucall uc;
+ u64 actual;
+
+ TEST_ASSERT_KVM_EXIT_REASON(vcpu, KVM_EXIT_IO);
+ actual = get_ucall(vcpu, &uc);
+ if (actual == UCALL_ABORT)
+ REPORT_GUEST_ASSERT(uc);
+
+ TEST_ASSERT_EQ(actual, UCALL_DONE);
+}
+
+int main(int argc, char *argv[])
+{
+ gva_t svm_gva, npf_gva, boundary_page_gva, iopm_gva;
+ gpa_t npf_gpa, mmio_source_gpa, mmio_gpa, iopm_gpa;
+ struct userspace_mem_region *region;
+ struct kvm_vcpu *vcpu;
+ struct kvm_vm *vm;
+ u8 *movsb_insn;
+ u64 *pte;
+
+ TEST_REQUIRE(kvm_cpu_has(X86_FEATURE_SVM));
+ TEST_REQUIRE(kvm_cpu_has(X86_FEATURE_NPT));
+ TEST_REQUIRE(this_cpu_has(X86_FEATURE_DECODEASSISTS));
+ TEST_ASSERT(kvm_cpu_has(X86_FEATURE_DECODEASSISTS),
+ "KVM failed to expose DecodeAssists");
+ TEST_REQUIRE(kvm_has_cap(KVM_CAP_EXCEPTION_PAYLOAD));
+
+ vm = vm_create_with_one_vcpu(&vcpu, l1_guest_code);
+ vm_enable_cap(vm, KVM_CAP_EXCEPTION_PAYLOAD, 1);
+ prepare_boundary_outsb_code(vm);
+ vm_enable_npt(vm);
+ vcpu_alloc_svm(vm, &svm_gva);
+ iopm_gva = vm_alloc_pages(vm, TEST_IOPM_SIZE / PAGE_SIZE);
+ iopm_gpa = addr_gva2gpa(vm, iopm_gva);
+ memset(addr_gva2hva(vm, iopm_gva), 0, TEST_IOPM_SIZE);
+ npf_gva = (gva_t)&npf_target;
+ npf_gpa = addr_gva2gpa(vm, npf_gva);
+
+ tdp_identity_map_default_memslots(vm);
+ pte = tdp_get_pte(vm, npf_gpa);
+ *pte &= ~PTE_PRESENT_MASK(&vm->stage2_mmu);
+ region = memslot2region(vm, 0);
+ mmio_gpa = region->region.guest_phys_addr +
+ region->region.memory_size + PAGE_SIZE;
+ mmio_source_gpa = addr_gva2gpa(vm, (gva_t)&mmio_source);
+ pte = tdp_get_pte(vm, mmio_source_gpa);
+ *pte = (*pte & ~PHYSICAL_PAGE_MASK) | mmio_gpa;
+
+ boundary_page_gva = (gva_t)&boundary_outsb_code[PAGE_SIZE];
+ pte = vm_get_pte(vm, boundary_page_gva);
+ *pte &= ~PTE_PRESENT_MASK(&vm->mmu);
+
+ vcpu_args_set(vcpu, 3, svm_gva, npf_gpa, iopm_gpa);
+
+ /* Complete the MOVSB source read. */
+ vcpu_run(vcpu);
+ complete_mmio_read(vcpu, mmio_gpa, 0xa5);
+ movsb_insn = addr_gva2hva(vm, (gva_t)l2_movsb_insn);
+ TEST_ASSERT_EQ(movsb_insn[0], MOVSB_OPCODE);
+ movsb_insn[0] = NOP_OPCODE;
+ vcpu_run(vcpu);
+ complete_mmio_read(vcpu, mmio_gpa, 0x5a);
+ queue_userspace_pf(vcpu);
+ vcpu_run(vcpu);
+ assert_ucall_done(vcpu);
+
+ kvm_vm_free(vm);
+ return 0;
+}
--
2.43.7
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