Re: [PATCH 0/2] KVM: x86: Fix lost nested APF VM-Exits

[Sean Christopherson]

On Fri, 02 Oct 2026 05:41:43 +0000, Loc Nguyen wrote:
> A nested asynchronous page fault delivered to L1 as a synthetic #PF
> VM-Exit can be lost after KVM queues the exception.  Most callers of
> kvm_queue_exception_vmexit() arrive through kvm_multiple_exception(),
> which requests event processing, but the nested APF path calls the
> helper directly.
> 
> Without KVM_REQ_EVENT, vcpu_enter_guest() can skip
> kvm_check_and_inject_events() and re-enter L2.  A later VM-Exit can then
> clear the pending exception while reconstructing vectoring state.  The
> APF reason remains PAGE_NOT_PRESENT, allowing a later regular #PF to
> consume the stale reason.
> 
> [...]

Applied the fix to kvm-x86 misc.  I'm going to hold off on the selftest for
the moment, I'd like to go straight to having it support both AMD and Intel.

Thanks!

[1/2] KVM: x86: Request event processing for exception VM-Exits
      https://github.com/kvm-x86/linux/commit/88b23a2e8286
[2/2] KVM: selftests: Add a test for lost nested APF VM-Exits
      [SKIP, for now]

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https://github.com/kvm-x86/linux/tree/next