linux-kernel - Re: [PATCH v2 0/3] Fix a lost async pagefault notification when the guest is using SMM

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Message-ID: <176278796977.917257.9553898354103958134.b4-ty@google.com>
Date: Mon, 10 Nov 2025 07:37:17 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, kvm@...r.kernel.org, 
	Maxim Levitsky <mlevitsk@...hat.com>
Cc: x86@...nel.org, Thomas Gleixner <tglx@...utronix.de>, Paolo Bonzini <pbonzini@...hat.com>, 
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org, 
	Borislav Petkov <bp@...en8.de>, "H. Peter Anvin" <hpa@...or.com>, Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH v2 0/3] Fix a lost async pagefault notification when the
 guest is using SMM

On Tue, 14 Oct 2025 23:32:55 -0400, Maxim Levitsky wrote:
> Recently we debugged a customer case in which the guest VM was showing
> tasks permanently stuck in the kvm_async_pf_task_wait_schedule.
> 
> This was traced to the incorrect flushing of the async pagefault queue,
> which was done during the real mode entry by the kvm_post_set_cr0.
> 
> This code, the kvm_clear_async_pf_completion_queue does wait for all #APF
> tasks to complete but then it proceeds to wipe the 'done' queue without
> notifying the guest.
> 
> [...]

Applied 2 and 3 to kvm-x86 misc.  The async #PF delivery path is also used by
the host-only version of async #PF (where KVM puts the vCPU into HLT instead of
letting the kernel schedule() in I/O), and so it's entirely expected that KVM
will dequeue completed async #PFs when the PV version is disabled.

https://lore.kernel.org/all/aQ5BiLBWGKcMe-mM@google.com

[1/3] KVM: x86: Warn if KVM tries to deliver an #APF completion when APF is not enabled
      [DROP]
[2/3] KVM: x86: Fix a semi theoretical bug in kvm_arch_async_page_present_queued
      https://github.com/kvm-x86/linux/commit/68c35f89d016
[3/3] KVM: x86: Fix the interaction between SMM and the asynchronous pagefault
      https://github.com/kvm-x86/linux/commit/ab4e41eb9fab

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