Re: [PATCH v3 1/2] x86/uaccess: Extend CMPXCHG user helpers to 128-bit operands

[Dave Hansen]

On 8/26/26 00:00, Sairaj Kodilkar wrote:
> Extend the existing user CMPXCHG helpers to support 16-byte operands on
> x86-64, using LOCK_PREFIX "cmpxchg16b".  This mirrors the existing
> __try_cmpxchg64_user_asm() / cmpxchg8b path provided for 32-bit kernels,
> where KVM needs an atomic compare-exchange wider than the generic
> cmpxchg helper can provide.

Please take a good look at the Sashiko review:

https://sashiko.dev/#/patchset/20260826070004.8100-2-sarunkod%40amd.com

It looks like the "A" constraint isn't one that you can cleanly mirror
from cmpxchg8b => cmpxchg16b.

Uros, any chance you can give these a good once-over? This seems to be
just the kind of thing you've been fixing up lately. It would be nice to
get them right the first time.