linux-kernel - Re: [PATCH] KVM: x86/mmu: Only zap valid non-mirror roots in kvm_zap_gfn

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Message-ID: <CABgObfa=t1dGR5cEhbUqVWTD03vZR4QrzEUgHxq+3JJ7YsA9pA@mail.gmail.com>
Date: Tue, 7 Jan 2025 15:01:05 +0100
From: Paolo Bonzini <pbonzini@...hat.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Yan Zhao <yan.y.zhao@...el.com>, rick.p.edgecombe@...el.com, 
	binbin.wu@...ux.intel.com, linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH] KVM: x86/mmu: Only zap valid non-mirror roots in kvm_zap_gfn_range()

On Tue, Jan 7, 2025 at 12:49 AM Sean Christopherson <seanjc@...gle.com> wrote:
> On Mon, Dec 23, 2024, Yan Zhao wrote:
> > On Sun, Dec 22, 2024 at 08:28:56PM +0100, Paolo Bonzini wrote:
> > > I think we should treat honoring of guest PAT like zap-memslot-only,
> > > and make it a quirk that TDX disables.  Making it a quirk adds a bit of
> > > complexity, but it documents why the code exists and it makes it easy for
> > > TDX to disable it.
>
> Belated +1.  Adding a quirk for honoring guest PAT was on my todo list.  A quirk
> also allows setups that don't provide a Bochs device to honor guest PAT, which
> IIRC is needed for virtio-gpu with a non-snooping graphics device.
>
> > Thanks! Will do in this way after the new year.
>
> Nice!  One oddity to keep in mind when documenting the quirk is that KVM always
> honors guest PAT when running on AMD.  :-/

And also when implementing it - the quirk should be absent on AMD.

Paolo