linux-kernel - Re: [PATCH 00/21] TDX/SNP part 1 of n, for 6.9

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Message-ID: <Zd91v2DeQmV0yQ1R@google.com>
Date: Wed, 28 Feb 2024 10:04:47 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Paolo Bonzini <pbonzini@...hat.com>
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org, michael.roth@....com, 
	isaku.yamahata@...el.com, thomas.lendacky@....com
Subject: Re: [PATCH 00/21] TDX/SNP part 1 of n, for 6.9

On Wed, Feb 28, 2024, Paolo Bonzini wrote:
> On Wed, Feb 28, 2024 at 5:39 PM Sean Christopherson <seanjc@...gle.com> wrote:
> > > > This doesn't work.  The ENC flag gets set on any SNP *capable* CPU, which results
> > > > in false positives for SEV and SEV-ES guests[*].
> > >
> > > You didn't look at the patch did you? :)
> >
> > Guilty, sort of.  I looked (and tested) the patch from the TDX series, but I didn't
> > look at what you postd.  But it's a moot point, because now I did look at what you
> > posted, and it's still broken :-)
> >
> > > It does check for has_private_mem (alternatively I could have dropped the bit
> > > in SVM code for SEV and SEV-ES guests).
> >
> > The problem isn't with *KVM* setting the bit, it's with *hardware* setting the
> > bit for SEV and SEV-ES guests.  That results in this:
> >
> >   .is_private = vcpu->kvm->arch.has_private_mem && (err & PFERR_GUEST_ENC_MASK),
> >
> > marking the fault as private.  Which, in a vacuum, isn't technically wrong, since
> > from hardware's perspective the vCPU access was "private".  But from KVM's
> > perspective, SEV and SEV-ES guests don't have private memory
> 
> vcpu->kvm->arch.has_private_mem is the flag from the SEV VM types
> series. It's false on SEV and SEV-ES VMs, therefore fault->is_private
> is going to be false as well. Is it ENOCOFFEE for you or ENODINNER for
> me? :)

*sigh*, ENOCOFFEE.