linux-kernel - Re: [PATCH] x86/coco, x86/sev: Use cpu_feature

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Date:   Tue, 5 Dec 2023 20:16:43 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Tom Lendacky <thomas.lendacky@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-coco@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/coco, x86/sev: Use cpu_feature_enabled() to detect
 SEV guest flavor

On Tue, Dec 05, 2023 at 05:00:35PM +0100, Borislav Petkov wrote:
> On Tue, Dec 05, 2023 at 06:14:37PM +0300, Kirill A. Shutemov wrote:
> > My point is that if you need to check for SEV you need to check SEV, not
> > CC_ATTR. CC_ATTRs only make sense in generic code that deals with multiple
> > CoCo environments.
> 
> That makes more sense.
> 
> So that commit already says "If future support is added for other
> memory encryption technologies, the use of CC_ATTR_GUEST_MEM_ENCRYPT
> can be updated, as required."
> 
> And what this test needs to do is to check:
> 
> 	if (guest type >= SEV)
> 
> meaning SEV and -ES and -SNP.
> 
> I'm wondering if we should export amd_cc_platform_has() for such
> cases...

What's wrong with using X86_FEATURE_* here?

X86_FEATURE_SEV_GUEST is set for all SEVs. X86_FEATURE_SEV_ES_GUEST and
X86_FEATURE_SEV_SNP_GUEST can be used to test specific flavor.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov