linux-kernel - Re: [PATCH v5 06/14] x86/ioremap: Support hypervisor specified range to map as encrypted

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Message-ID: <Y/adN3GQJTdDPmS8@google.com>
Date:   Wed, 22 Feb 2023 14:54:47 -0800
From:   Sean Christopherson <seanjc@...gle.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     "Michael Kelley (LINUX)" <mikelley@...rosoft.com>,
        Dave Hansen <dave.hansen@...el.com>,
        "hpa@...or.com" <hpa@...or.com>, KY Srinivasan <kys@...rosoft.com>,
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Subject: Re: [PATCH v5 06/14] x86/ioremap: Support hypervisor specified range
 to map as encrypted

On Wed, Feb 22, 2023, Borislav Petkov wrote:
> On Wed, Feb 22, 2023 at 02:13:44PM -0800, Sean Christopherson wrote:
> > Because vTOM is a hardware feature, whereas the IO-APIC and vTPM being accessible
> > via private memory are software features.  It's very possible to emulate the
> > IO-APIC in trusted code without vTOM.
> 
> I know, but their use case is dictated by the fact that they're using
> a SNP guest *with* vTOM as a SEV feature. And so their guest does
> IO-APIC and vTPM *with* the vTOM SEV feature. That's what I'm trying to
> model.

Why?  I genuinely don't understand the motivation for bundling all of this stuff
under a single "feature".  To me, that's like saying Haswell or Zen2 is a "feature",
but outside of a very few cases where the exact uarch truly matters, nothing pivots
on FMS because the CPU type is not a single feature.