From: David Laight <david.laight.linux@gmail.com>
To: Borislav Petkov <bp@alien8.de>
Cc: Mauricio Faria de Oliveira <mfo@igalia.com>,
Thomas Gleixner <tglx@kernel.org>, Ingo Molnar <mingo@redhat.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
Juergen Gross <jgross@suse.com>,
Alexey Dobriyan <adobriyan@gmail.com>,
Boris Ostrovsky <boris.ostrovsky@oracle.com>,
Jan Beulich <jbeulich@suse.com>, Brian Gerst <brgerst@gmail.com>,
kernel-dev@igalia.com, linux-kernel@vger.kernel.org,
xen-devel@lists.xenproject.org
Subject: Re: [PATCH v9 4/5] x86/cpuid: fix unbootable VMs by really inlining memcmp() in hypervisor_cpuid_base()
Date: Tue, 15 Sep 2026 09:43:39 +0100 [thread overview]
Message-ID: <20260915094339.39a83b54@pumpkin> (raw)
In-Reply-To: <20260915051155.GGaqjTm7yIluwxZ80x@fat_crate.local>
On Mon, 14 Sep 2026 22:11:55 -0700
Borislav Petkov <bp@alien8.de> wrote:
> On Mon, Sep 14, 2026 at 08:22:08AM -0300, Mauricio Faria de Oliveira wrote:
> > In the review of the original patchset (fixed by this series) it is
> > mentioned that a compiler might turn it into a memcmp() [1] -- and thus
> > revert back to the same issue.
> >
> > [1] https://lore.kernel.org/all/877ccz12ab.ffs@tglx/
>
> Hmm, never heard that before but that doesn't mean anything. Probably should
> mention it in one of the commit messages so that we know for the future...
>
It definitely has a habit of converting copy loops to memcpy().
Annoying when they are short.
But usually easily avoidable by sprinkling 'volatile' or barrier() in the
right places.
David
next prev parent reply other threads:[~2026-09-15 8:43 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-08-22 18:33 [PATCH v9 0/5] x86/pvh: fix unbootable VMs again (PVH + KASAN) Mauricio Faria de Oliveira
2026-08-22 18:33 ` [PATCH v9 1/5] x86/boot: Remove "cc" clobber from memcmp() Mauricio Faria de Oliveira
2026-09-01 13:16 ` Jan Beulich
2026-09-02 8:33 ` David Laight
2026-09-02 14:18 ` H. Peter Anvin
2026-09-02 2:31 ` Borislav Petkov
2026-09-02 13:29 ` Michael Matz
2026-09-02 13:48 ` Mauricio Faria de Oliveira
2026-09-03 0:01 ` Borislav Petkov
2026-09-03 0:07 ` Mauricio Faria de Oliveira
2026-09-03 0:39 ` Borislav Petkov
2026-09-03 8:40 ` David Laight
2026-09-02 23:58 ` Borislav Petkov
2026-08-22 18:33 ` [PATCH v9 2/5] x86/asm, x86/boot: expose inline memcmp() Mauricio Faria de Oliveira
2026-09-06 17:01 ` Borislav Petkov
2026-09-06 18:15 ` H. Peter Anvin
2026-09-08 18:04 ` Mauricio Faria de Oliveira
2026-09-08 19:32 ` Borislav Petkov
2026-09-08 21:06 ` Mauricio Faria de Oliveira
2026-09-10 3:38 ` Borislav Petkov
2026-09-10 13:07 ` Mauricio Faria de Oliveira
2026-09-10 14:03 ` H. Peter Anvin
2026-09-08 23:16 ` H. Peter Anvin
2026-09-09 8:38 ` David Laight
2026-09-09 13:43 ` H. Peter Anvin
2026-09-09 19:28 ` David Laight
2026-09-09 19:33 ` H. Peter Anvin
2026-09-09 21:39 ` David Laight
2026-09-09 23:12 ` H. Peter Anvin
2026-09-08 17:57 ` Mauricio Faria de Oliveira
2026-08-22 18:33 ` [PATCH v9 3/5] x86/asm: group inline string functions Mauricio Faria de Oliveira
2026-08-22 18:33 ` [PATCH v9 4/5] x86/cpuid: fix unbootable VMs by really inlining memcmp() in hypervisor_cpuid_base() Mauricio Faria de Oliveira
2026-09-11 4:38 ` Borislav Petkov
2026-09-14 11:22 ` Mauricio Faria de Oliveira
2026-09-15 5:11 ` Borislav Petkov
2026-09-15 8:43 ` David Laight [this message]
2026-08-22 18:33 ` [PATCH v9 5/5] x86/pvh: fix unbootable VMs by really inlining memset() in xen_prepare_pvh() Mauricio Faria de Oliveira
2026-09-11 4:39 ` Borislav Petkov
2026-09-14 11:40 ` Mauricio Faria de Oliveira
2026-09-15 5:26 ` Borislav Petkov
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