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

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Message-ID: <20231205150012.6lma2wzcellr7pz7@box.shutemov.name>
Date:   Tue, 5 Dec 2023 18:00:12 +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 03:46:19PM +0100, Borislav Petkov wrote:
> On Tue, Dec 05, 2023 at 05:37:38PM +0300, Kirill A. Shutemov wrote:
> > The SEV code uses cc_platform_has() checks to detect the SEV flavor.
> > However, these checks can sometimes produce false positives depending on
> > the context.
> > 
> > For example, sev_map_percpu_data() uses CC_ATTR_GUEST_MEM_ENCRYPT to
> > detect SEV guest, but this check will also pass for TDX guests.
> 
> Well, a function prefixed with "sev_" should check cc_vendor first...

I don't think cc_platform_has() is the right check. On TDX side we use
X86_FEATURE_TDX_GUEST for this and it works better than stretching
CC_ATTRs beyond their meaning.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov