linux-kernel - Re: [PATCH 2/4] KVM: x86/mmu: Fully re-evaluate MMIO caching when SPTE masks change

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Message-ID: <YufgCR9CpeoVWKF7@google.com>
Date:   Mon, 1 Aug 2022 14:15:37 +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, Michael Roth <michael.roth@....com>,
        Tom Lendacky <thomas.lendacky@....com>
Subject: Re: [PATCH 2/4] KVM: x86/mmu: Fully re-evaluate MMIO caching when
 SPTE masks change

On Mon, Aug 01, 2022, Kai Huang wrote:
> On Fri, 2022-07-29 at 15:07 +0000, Sean Christopherson wrote:
> > Lastly, in prepration for TDX, enable_mmio_caching should be changed to key off
> > of the _mask_, not the value.  E.g. for TDX, the value will be '0', but the mask
> > should be SUPPRESS_VE | RWX.
> 
> Agreed.  But perhaps in another patch.  We need to re-define what does
> mask/value mean to enable_mmio_caching.

There's no need to redefine what they mean, the only change that needs to be made
is handle the scenario where desire value is '0'.  Maybe that's all you mean by
"redefine"?

Another thing to note is that only the value needs to be per-VM, the mask can be
KVM-wide, i.e. "mask = SUPPRESS_VE | RWX" will work for TDX and non-TDX VMs when
EPT is enabled.