Re: [PATCH v3 0/8] x86: Remove cpu_has_xfeatures() and add AVX-512 xor_gen()

[Eric Biggers <ebiggers@kernel.org>]

On Thu, Aug 13, 2026 at 05:35:17PM -0700, Borislav Petkov wrote:
> On Wed, Aug 12, 2026 at 07:14:58PM -0700, Eric Biggers wrote:
> > This series consolidates and cleans up how the kernel handles CPU
> > feature flags for AVX and AVX-512 when the underlying OS or hypervisor
> > (if any) doesn't enable the required xstate features in XCR0.
> > 
> > Specifically, it makes the checks for xstate features be done in a
> > single place at boot time for both UML and native x86, instead of
> > everywhere kernel code wants to check for AVX or AVX-512 support.
> > 
> > Patch 8 then adds an AVX-512 optimized implementation of xor_gen() for
> > RAID, which had been blocked on confusion around cpu_has_xfeatures() and
> > its lack of implementation on UML.
> 
> Sashiko complains about a missing VZEROUPPER there in patch 8:
> 
> https://sashiko.dev/#/patchset/20260813021506.55129-1-ebiggers%40kernel.org

Yeah, missing vzeroupper is a common mistake...  All the other code in
lib/raid/ that uses ymm and zmm registers misses it too.  I've fixed
various instances of this in the crypto code before, but no one ever
checked the RAID code.  I guess I'll send out a v4 that fixes patch 8,
and also separate patches that try to fix all the existing instances of
missing vzeroupper.  Besides lib/raid/, some also have slipped in in
arch/x86/crypto/aria-* and net/netfilter/nft_set_pipapo_avx2.c.

- Eric