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

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Date:   Tue, 5 Dec 2023 17:00:35 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
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 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...

The logic being, we're calling a SEV-specific function so using
cc_platform_has() in there is the wrong layer.

Tom?

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette