From: Sean Christopherson <seanjc@google.com>
To: Sean Christopherson <seanjc@google.com>,
Paolo Bonzini <pbonzini@redhat.com>
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
Jim Mattson <jmattson@google.com>,
Maxim Levitsky <mlevitsk@redhat.com>,
Oliver Upton <oupton@google.com>, Peter Shier <pshier@google.com>
Subject: [PATCH v2 21/24] KVM: VMX: Update MTF and ICEBP comments to document KVM's subtle behavior
Date: Fri, 15 Jul 2022 20:42:23 +0000 [thread overview]
Message-ID: <20220715204226.3655170-22-seanjc@google.com> (raw)
In-Reply-To: <20220715204226.3655170-1-seanjc@google.com>
Document the oddities of ICEBP interception (trap-like #DB is intercepted
as a fault-like exception), and how using VMX's inner "skip" helper
deliberately bypasses the pending MTF and single-step #DB logic.
No functional change intended.
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/vmx/vmx.c | 16 +++++++++++-----
1 file changed, 11 insertions(+), 5 deletions(-)
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 5302b046110f..de6fcfa0ef02 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1578,9 +1578,13 @@ static void vmx_update_emulated_instruction(struct kvm_vcpu *vcpu)
/*
* Per the SDM, MTF takes priority over debug-trap exceptions besides
- * T-bit traps. As instruction emulation is completed (i.e. at the
- * instruction boundary), any #DB exception pending delivery must be a
- * debug-trap. Record the pending MTF state to be delivered in
+ * TSS T-bit traps and ICEBP (INT1). KVM doesn't emulate T-bit traps
+ * or ICEBP (in the emulator proper), and skipping of ICEBP after an
+ * intercepted #DB deliberately avoids single-step #DB and MTF updates
+ * as ICEBP is higher priority than both. As instruction emulation is
+ * completed at this point (i.e. KVM is at the instruction boundary),
+ * any #DB exception pending delivery must be a debug-trap of lower
+ * priority than MTF. Record the pending MTF state to be delivered in
* vmx_check_nested_events().
*/
if (nested_cpu_has_mtf(vmcs12) &&
@@ -5084,8 +5088,10 @@ static int handle_exception_nmi(struct kvm_vcpu *vcpu)
* instruction. ICEBP generates a trap-like #DB, but
* despite its interception control being tied to #DB,
* is an instruction intercept, i.e. the VM-Exit occurs
- * on the ICEBP itself. Note, skipping ICEBP also
- * clears STI and MOVSS blocking.
+ * on the ICEBP itself. Use the inner "skip" helper to
+ * avoid single-step #DB and MTF updates, as ICEBP is
+ * higher priority. Note, skipping ICEBP still clears
+ * STI and MOVSS blocking.
*
* For all other #DBs, set vmcs.PENDING_DBG_EXCEPTIONS.BS
* if single-step is enabled in RFLAGS and STI or MOVSS
--
2.37.0.170.g444d1eabd0-goog
next prev parent reply other threads:[~2022-07-15 20:45 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-15 20:42 [PATCH v2 00/24] KVM: x86: Event/exception fixes and cleanups Sean Christopherson
2022-07-15 20:42 ` [PATCH v2 01/24] KVM: nVMX: Unconditionally purge queued/injected events on nested "exit" Sean Christopherson
2022-07-15 20:42 ` [PATCH v2 02/24] KVM: VMX: Drop bits 31:16 when shoving exception error code into VMCS Sean Christopherson
2022-07-18 13:04 ` Maxim Levitsky
2022-07-18 16:37 ` Sean Christopherson
2022-07-15 20:42 ` [PATCH v2 03/24] KVM: x86: Don't check for code breakpoints when emulating on exception Sean Christopherson
2022-07-15 20:42 ` [PATCH v2 04/24] KVM: nVMX: Treat General Detect #DB (DR7.GD=1) as fault-like Sean Christopherson
2022-07-15 20:42 ` [PATCH v2 05/24] KVM: nVMX: Prioritize TSS T-flag #DBs over Monitor Trap Flag Sean Christopherson
2022-07-15 20:42 ` [PATCH v2 06/24] KVM: x86: Treat #DBs from the emulator as fault-like (code and DR7.GD=1) Sean Christopherson
2022-07-15 20:42 ` [PATCH v2 07/24] KVM: x86: Use DR7_GD macro instead of open coding check in emulator Sean Christopherson
2022-07-15 20:42 ` [PATCH v2 08/24] KVM: nVMX: Ignore SIPI that arrives in L2 when vCPU is not in WFS Sean Christopherson
2022-07-15 20:42 ` [PATCH v2 09/24] KVM: nVMX: Unconditionally clear mtf_pending on nested VM-Exit Sean Christopherson
2022-07-18 13:04 ` Maxim Levitsky
2022-07-15 20:42 ` [PATCH v2 10/24] KVM: VMX: Inject #PF on ENCLS as "emulated" #PF Sean Christopherson
2022-07-15 20:42 ` [PATCH v2 11/24] KVM: x86: Rename kvm_x86_ops.queue_exception to inject_exception Sean Christopherson
2022-07-15 20:42 ` [PATCH v2 12/24] KVM: x86: Make kvm_queued_exception a properly named, visible struct Sean Christopherson
2022-07-15 20:42 ` [PATCH v2 13/24] KVM: x86: Formalize blocking of nested pending exceptions Sean Christopherson
2022-07-15 20:42 ` [PATCH v2 14/24] KVM: x86: Use kvm_queue_exception_e() to queue #DF Sean Christopherson
2022-07-15 20:42 ` [PATCH v2 15/24] KVM: x86: Hoist nested event checks above event injection logic Sean Christopherson
2022-07-15 20:42 ` [PATCH v2 16/24] KVM: x86: Evaluate ability to inject SMI/NMI/IRQ after potential VM-Exit Sean Christopherson
2022-07-15 20:42 ` [PATCH v2 17/24] KVM: nVMX: Add a helper to identify low-priority #DB traps Sean Christopherson
2022-07-18 13:04 ` Maxim Levitsky
2022-07-15 20:42 ` [PATCH v2 18/24] KVM: nVMX: Document priority of all known events on Intel CPUs Sean Christopherson
2022-07-18 13:04 ` Maxim Levitsky
2022-07-15 20:42 ` [PATCH v2 19/24] KVM: x86: Morph pending exceptions to pending VM-Exits at queue time Sean Christopherson
2022-07-18 13:05 ` Maxim Levitsky
2022-07-15 20:42 ` [PATCH v2 20/24] KVM: x86: Treat pending TRIPLE_FAULT requests as pending exceptions Sean Christopherson
2022-07-15 20:42 ` Sean Christopherson [this message]
2022-07-18 13:05 ` [PATCH v2 21/24] KVM: VMX: Update MTF and ICEBP comments to document KVM's subtle behavior Maxim Levitsky
2022-07-15 20:42 ` [PATCH v2 22/24] KVM: x86: Rename inject_pending_events() to kvm_check_and_inject_events() Sean Christopherson
2022-07-18 13:05 ` Maxim Levitsky
2022-07-15 20:42 ` [PATCH v2 23/24] KVM: selftests: Use uapi header to get VMX and SVM exit reasons/codes Sean Christopherson
2022-07-15 20:42 ` [PATCH v2 24/24] KVM: selftests: Add an x86-only test to verify nested exception queueing Sean Christopherson
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