linux-kernel - Re: [PATCH v7 05/22] x86/sev: Move GHCB page based HV communication out of startup code

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Message-ID: <CAMj1kXHrsR+qGA5a8s1GWsramZ_QEdKWgG2ehb3+kE=5+vaicw@mail.gmail.com>
Date: Mon, 1 Sep 2025 16:26:40 +0200
From: Ard Biesheuvel <ardb@...nel.org>
To: Borislav Petkov <bp@...en8.de>
Cc: Ard Biesheuvel <ardb+git@...gle.com>, linux-kernel@...r.kernel.org, 
	linux-efi@...r.kernel.org, x86@...nel.org, Ingo Molnar <mingo@...nel.org>, 
	Kevin Loughlin <kevinloughlin@...gle.com>, Tom Lendacky <thomas.lendacky@....com>, 
	Josh Poimboeuf <jpoimboe@...nel.org>, Peter Zijlstra <peterz@...radead.org>, 
	Nikunj A Dadhania <nikunj@....com>
Subject: Re: [PATCH v7 05/22] x86/sev: Move GHCB page based HV communication
 out of startup code

On Mon, 1 Sept 2025 at 16:26, Borislav Petkov <bp@...en8.de> wrote:
>
> On Mon, Sep 01, 2025 at 04:02:04PM +0200, Ard Biesheuvel wrote:
> > Are you sure this can be removed? It is tested in other places too
> > (arch/x86/coco/sev/core.c), and AIUI, it is a Linux defined CPU
> > feature so it will never be set automatically.
>
> It it set in scattered.c for the "late" code like sev/core.c:
>
> arch/x86/kernel/cpu/scattered.c:51:     { X86_FEATURE_COHERENCY_SFW_NO,         CPUID_EBX, 31, 0x8000001f, 0 },
>
> Tom added it to boot/cpuflags.c, in addition, for the early testing which
> we're doing differently now.
>

Ah ok, yes that makes sense.