From: Sean Christopherson <seanjc@google.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
Oliver Upton <oupton@google.com>, Peter Shier <pshier@google.com>
Subject: [PATCH 19/21] KVM: VMX: Update MTF and ICEBP comments to document KVM's subtle behavior
Date: Fri, 11 Mar 2022 03:27:59 +0000 [thread overview]
Message-ID: <20220311032801.3467418-20-seanjc@google.com> (raw)
In-Reply-To: <20220311032801.3467418-1-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 0420bc6d418a..ae88d42289ce 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1570,9 +1570,13 @@ 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) &&
@@ -4924,8 +4928,10 @@ 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
--
2.35.1.723.g4982287a31-goog
next prev parent reply other threads:[~2022-03-11 3:29 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-11 3:27 [PATCH 00/21] KVM: x86: Event/exception fixes and cleanups Sean Christopherson
2022-03-11 3:27 ` [PATCH 01/21] KVM: x86: Return immediately from x86_emulate_instruction() on code #DB Sean Christopherson
2022-03-11 3:27 ` [PATCH 02/21] KVM: nVMX: Unconditionally purge queued/injected events on nested "exit" Sean Christopherson
2022-03-11 3:27 ` [PATCH 03/21] KVM: VMX: Drop bits 31:16 when shoving exception error code into VMCS Sean Christopherson
2022-03-11 3:27 ` [PATCH 04/21] KVM: x86: Don't check for code breakpoints when emulating on exception Sean Christopherson
2022-03-11 3:27 ` [PATCH 05/21] KVM: nVMX: Treat General Detect #DB (DR7.GD=1) as fault-like Sean Christopherson
2022-03-11 3:27 ` [PATCH 06/21] KVM: nVMX: Prioritize TSS T-flag #DBs over Monitor Trap Flag Sean Christopherson
2022-03-11 3:27 ` [PATCH 07/21] KVM: x86: Treat #DBs from the emulator as fault-like (code and DR7.GD=1) Sean Christopherson
2022-03-11 3:27 ` [PATCH 08/21] KVM: x86: Use DR7_GD macro instead of open coding check in emulator Sean Christopherson
2022-03-11 3:27 ` [PATCH 09/21] KVM: nVMX: Ignore SIPI that arrives in L2 when vCPU is not in WFS Sean Christopherson
2022-03-11 3:27 ` [PATCH 10/21] KVM: nVMX: Unconditionally clear mtf_pending on nested VM-Exit Sean Christopherson
2022-03-11 3:27 ` [PATCH 11/21] KVM: VMX: Inject #PF on ENCLS as "emulated" #PF Sean Christopherson
2022-03-11 3:27 ` [PATCH 12/21] KVM: x86: Rename kvm_x86_ops.queue_exception to inject_exception Sean Christopherson
2022-03-11 3:27 ` [PATCH 13/21] KVM: x86: Make kvm_queued_exception a properly named, visible struct Sean Christopherson
2022-03-11 3:27 ` [PATCH 14/21] KVM: x86: Formalize blocking of nested pending exceptions Sean Christopherson
2022-03-11 3:27 ` [PATCH 15/21] KVM: x86: Use kvm_queue_exception_e() to queue #DF Sean Christopherson
2022-03-11 3:27 ` [PATCH 16/21] KVM: x86: Hoist nested event checks above event injection logic Sean Christopherson
2022-03-11 3:27 ` [PATCH 17/21] KVM: x86: Evaluate ability to inject SMI/NMI/IRQ after potential VM-Exit Sean Christopherson
2022-03-11 3:27 ` [PATCH 18/21] KVM: x86: Morph pending exceptions to pending VM-Exits at queue time Sean Christopherson
2022-03-11 3:27 ` Sean Christopherson [this message]
2022-03-11 3:28 ` [PATCH 20/21] KVM: selftests: Use uapi header to get VMX and SVM exit reasons/codes Sean Christopherson
2022-03-11 3:28 ` [PATCH 21/21] KVM: selftests: Add an x86-only test to verify nested exception queueing Sean Christopherson
2022-03-11 16:30 ` [PATCH 00/21] KVM: x86: Event/exception fixes and cleanups Maciej S. Szmigiero
2022-03-13 9:22 ` Maxim Levitsky
2022-03-24 21:31 ` Sean Christopherson
2022-03-25 21:25 ` Maciej S. Szmigiero
2022-03-25 23:02 ` Sean Christopherson
2022-03-26 0:21 ` Maciej S. Szmigiero
2022-03-27 15:06 ` Maxim Levitsky
2022-03-28 17:50 ` Sean Christopherson
2022-03-29 10:45 ` Maxim Levitsky
2022-03-29 15:43 ` Sean Christopherson
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20220311032801.3467418-20-seanjc@google.com \
--to=seanjc@google.com \
--cc=jmattson@google.com \
--cc=joro@8bytes.org \
--cc=kvm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=oupton@google.com \
--cc=pbonzini@redhat.com \
--cc=pshier@google.com \
--cc=vkuznets@redhat.com \
--cc=wanpengli@tencent.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox
all inboxes | Powered by JetHome®