linux-kernel - Re: [PATCH] KVM: x86/mmu: Add sanity check that MMIO SPTE mask doesn't overlap gen

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Date:   Wed, 3 Aug 2022 22:49:20 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Kai Huang <kai.huang@...el.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: x86/mmu: Add sanity check that MMIO SPTE mask
 doesn't overlap gen

On Thu, Aug 04, 2022, Kai Huang wrote:
> On Wed, 2022-08-03 at 21:33 +0000, Sean Christopherson wrote:
> > Add compile-time and init-time sanity checks to ensure that the MMIO SPTE
> > mask doesn't overlap the MMIO SPTE generation.  The generation currently
> > avoids using bit 63, but that's as much coincidence as it is strictly
> > necessarly.  That will change in the future, as TDX support will require
> > setting bit 63 (SUPPRESS_VE) in the mask.  Explicitly carve out the bits
> > that are allowed in the mask so that any future shuffling of SPTE MMIO
> > bits doesn't silently break MMIO caching.
> 
> Reviwed-by: Kai Huang <kai.huang@...el.com>
> 
> Btw, should you also check SPTE_MMU_PRESENT_MASK (or in another patch)?

Rats, I thought we already checked that, but it's only the MMIO generation that
checks for overlap.  I'll send a v2.