linux-kernel - Re: [GIT pull] x86/urgent for v6.16-rc7

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Message-ID: <CAHk-=wha6sXik-f0RC91TMbt4snau0jK+dPvQEMezGiVFDpKUQ@mail.gmail.com>
Date: Sun, 20 Jul 2025 11:35:00 -0700
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Thomas Gleixner <tglx@...utronix.de>, Ard Biesheuvel <ardb@...nel.org>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [GIT pull] x86/urgent for v6.16-rc7

On Sun, 20 Jul 2025 at 05:05, Thomas Gleixner <tglx@...utronix.de> wrote:
>
> A single fix for a GCC wreckage, which emits a KCSAN instrumentation call
> in __sev_es_nmi_complete() despite the function being annotated with
> 'noinstr'. As all functions in that source file are noinstr, exclude the
> whole file from KCSAN in the Makefile to cure it.

Hmm. I'm not entirely sure if this counts as a gcc bug.

In particular, look at the *declaration* of __sev_es_nmi_complete() in
<asm/sev.h>, and note the complete lack of 'noinstr':

    extern void __sev_es_nmi_complete(void);

and I wonder if it might be the case that gcc might pick up the lack
of 'noinstr' from the declaration, even if it's there in the
definition..

The fix for this obviously ends up working and is fine regardless, but
it's _possible_ that this is self-inflicted pain rather than an
outright compiler bug. Because having a declaration and a definition
that doesn't match sounds like a bad idea in the first place.

               Linus