From: Chao Gao <chao.gao@intel.com>
To: Venkatesh Srinivas <venkateshs@chromium.org>
Cc: <kvm@vger.kernel.org>, <stable@vger.kernel.org>,
David Matlack <dmatlack@google.com>,
Sean Christopherson <seanjc@google.com>,
Jim Mattson <jmattson@google.com>,
James Houghton <jthoughton@google.com>
Subject: Re: [PATCH] KVM: x86: Only reset TSC Deadline Timer in apic_timer_expired on KVM_RUN
Date: Mon, 20 Jul 2026 16:37:08 +0800 [thread overview]
Message-ID: <al3eNJFTJur4FI8T@intel.com> (raw)
In-Reply-To: <20260715234234.15382-2-venkateshs@chromium.org>
On Wed, Jul 15, 2026 at 11:42:35PM +0000, Venkatesh Srinivas wrote:
>Fixes a lost timer interrupt issue if:
>1) We are on an Intel platform w/ a VMX preemption timer && APICv
>2) A VMM calls KVM_GET_LAPIC before KVM_GET_MSRS to save vCPU state
>3) The thread executing the two calls migrates CPUs between the two calls
>
>After migration across CPUs, KVM_GET_MSRS calls vcpu_load, posting the
>interrupt and clearing the MSR:
>vcpu_load() ->
> kvm_arch_vcpu_load() ->
> kvm_lapic_restart_hv_timer() ->
> start_hv_timer() ->
> apic_timer_expired() ->
> kvm_apic_inject_pending_timer_irqs()
> . post interrupt into the LAPIC state
> . clear IA32_TSCDEADLINE
>
>The saved LAPIC state will be missing the pending interrupt and the saved
>MSR will be zero. Oops.
>
>Fix by only posting an interrupt when we're attempting to enter the guest
>(vcpu->wants_to_run == true), not for vcpu_load from other paths.
>
>Assisted-by: gemini:gemini-3.1-pro-preview
>Debugged-by: David Matlack <dmatlack@google.com>
>Debugged-by: Sean Christopherson <seanjc@google.com>
>Debugged-by: Jim Mattson <jmattson@google.com>
>Debugged-by: James Houghton <jthoughton@google.com>
>Signed-off-by: Venkatesh Srinivas <venkateshs@chromium.org>
Reviewed-by: Chao Gao <chao.gao@intel.com>
prev parent reply other threads:[~2026-07-20 8:37 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-15 23:42 [PATCH] KVM: x86: Only reset TSC Deadline Timer in apic_timer_expired on KVM_RUN Venkatesh Srinivas
2026-07-16 1:14 ` James Houghton
2026-07-20 13:51 ` Paolo Bonzini
2026-07-20 8:37 ` Chao Gao [this message]
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=al3eNJFTJur4FI8T@intel.com \
--to=chao.gao@intel.com \
--cc=dmatlack@google.com \
--cc=jmattson@google.com \
--cc=jthoughton@google.com \
--cc=kvm@vger.kernel.org \
--cc=seanjc@google.com \
--cc=stable@vger.kernel.org \
--cc=venkateshs@chromium.org \
/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