From: David Laight <david.laight.linux@gmail.com>
To: Arnd Bergmann <arnd@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>, Arnd Bergmann <arnd@arndb.de>,
Richard Weinberger <richard@nod.at>,
Anton Ivanov <anton.ivanov@cambridgegreys.com>,
Johannes Berg <johannes@sipsolutions.net>,
Thomas Gleixner <tglx@kernel.org>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
"H. Peter Anvin" <hpa@zytor.com>,
Peter Zijlstra <peterz@infradead.org>,
Will Deacon <will@kernel.org>, Boqun Feng <boqun@kernel.org>,
Gary Guo <gary@garyguo.net>, Yury Norov <yury.norov@gmail.com>,
Rasmus Villemoes <linux@rasmusvillemoes.dk>,
Boris Ostrovsky <boris.ostrovsky@oracle.com>,
Alexander Usyskin <alexander.usyskin@intel.com>,
Tony Nguyen <anthony.l.nguyen@intel.com>,
Przemek Kitszel <przemyslaw.kitszel@intel.com>,
x86@kernel.org, linux-kernel@vger.kernel.org,
linux-um@lists.infradead.org
Subject: Re: [PATCH 3/7] x86: make CX8 usage unconditional
Date: Sun, 8 Nov 2026 20:30:42 +0000 [thread overview]
Message-ID: <20261108203042.7e36f15b@pumpkin> (raw)
In-Reply-To: <20261105163440.2381661-4-arnd@kernel.org>
On Thu, 5 Nov 2026 17:34:34 +0100
Arnd Bergmann <arnd@kernel.org> wrote:
> From: Arnd Bergmann <arnd@arndb.de>
>
> All supported CPUs now provide the cmpxchg8b instruction, so remove
> all compile-time and runtime checks for its presence and the fallback
> implementation, to assume it just works.
Is it worth doing a run-time check early on any (trying) to output
a message and fail to boot?
There are probably a few other things the kernel could rely on, but
probably ought to do a check 'just in case'.
One that springs to mind is whether 'find first set' leaves the dest
unchanged for zero. There is a comment that 'at least some 486 didn't'
but assuming it can make code smaller.
(Basically you can do a double-width operation by putting the result
from the low word in the destination before doing the high word.)
But it would be nice to have one test case during boot.
David
next prev parent reply other threads:[~2026-11-08 20:30 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-11-05 16:34 [PATCH v2 0/7] x86-32 CPU configuration cleanups Arnd Bergmann
2026-11-05 16:34 ` [PATCH 1/7] x86: remove AMD Élan remnants Arnd Bergmann
2026-11-05 16:34 ` [PATCH 2/7] x86: make TSC usage unconditional Arnd Bergmann
2026-11-05 16:34 ` [PATCH 3/7] x86: make CX8 " Arnd Bergmann
2026-11-05 22:30 ` Uros Bizjak
2026-11-06 2:29 ` kernel test robot
2026-11-06 15:43 ` David Gow
2026-11-08 20:30 ` David Laight [this message]
2026-11-05 16:34 ` [PATCH 4/7] x86: require minimum 64 byte cache lines Arnd Bergmann
2026-11-05 16:34 ` [PATCH 5/7] x86: remove dependencies on CONFIG_M... CPU options Arnd Bergmann
2026-11-05 16:34 ` [PATCH 6/7] x86: remove dependencies on per-CPU options Arnd Bergmann
2026-11-05 16:34 ` [PATCH 7/7] x86: simplify 32-bit instruction set selection Arnd Bergmann
2026-11-05 20:17 ` H. Peter Anvin
2026-11-05 22:01 ` Arnd Bergmann
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