linux-kernel - Re: [PATCH] KVM: x86/mmu: Treat TDP MMU faults as spurious if access is already allowed

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Message-ID: <CAPpAL=zkBpqKYQp4-n-E+Ky9KBkqXN_Sw17GA-FRDLmJtVp+KA@mail.gmail.com>
Date: Thu, 19 Dec 2024 22:55:45 +0800
From: Lei Yang <leiyang@...hat.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: x86/mmu: Treat TDP MMU faults as spurious if access
 is already allowed

I tested this patch with the bug's reproducer, the problem has gone.

Tested-by: Lei Yang <leiyang@...hat.com>

On Thu, Dec 19, 2024 at 10:41 AM Sean Christopherson <seanjc@...gle.com> wrote:
>
> On Wed, 18 Dec 2024 13:36:11 -0800, Sean Christopherson wrote:
> > Treat slow-path TDP MMU faults as spurious if the access is allowed given
> > the existing SPTE to fix a benign warning (other than the WARN itself)
> > due to replacing a writable SPTE with a read-only SPTE, and to avoid the
> > unnecessary LOCK CMPXCHG and subsequent TLB flush.
> >
> > If a read fault races with a write fault, fast GUP fails for any reason
> > when trying to "promote" the read fault to a writable mapping, and KVM
> > resolves the write fault first, then KVM will end up trying to install a
> > read-only SPTE (for a !map_writable fault) overtop a writable SPTE.
> >
> > [...]
>
> Applied very quickly to kvm-x86 fixes, so that it can get at least one day in
> -next before I send it to Paolo.
>
> [1/1] KVM: x86/mmu: Treat TDP MMU faults as spurious if access is already allowed
>       https://github.com/kvm-x86/linux/commit/55f60a6498e7
>
> --
> https://github.com/kvm-x86/linux/tree/next
>