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

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Message-ID: <173457570836.3297396.12144430815948289089.b4-ty@google.com>
Date: Wed, 18 Dec 2024 18:40:40 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, leiyang@...hat.com
Subject: Re: [PATCH] KVM: x86/mmu: Treat TDP MMU faults as spurious if access
 is already allowed

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