Re: [PATCH 0/6] x86: add missing vzeroupper instructions

On Sat, 15 Aug 2026 13:57:44 -0700
Eric Biggers <[email protected]> wrote:

> Assembly code using YMM or ZMM registers is supposed to end with the
> vzeroupper instruction in order to avoid degrading the performance of
> any later SSE code.  Since this only affects performance and not
> correctness, it is sometimes overlooked.  Most kernel code does it
> correctly, but a few cases were missed.  This series fixes them.
> 
> It should be easiest to take the full series through the x86 tree.

Would it be better to an an unconditional vzeroupper in kernel_fpu_end()?
It could go in kernel_fpu_start() but that might have a bigger effect
on latency.
(I assume there is one in kernel_fpu_start() if it actually saves
the user registers?)

Looking the latency/uops seems reasonably on everything 'recent' except
zen-1 and knights-landing.
Although the microcode patch for zen-2 might make that a lot worse.

	David  


> 
> Eric Biggers (6):
>   xor: add missing vzeroupper to AVX code
>   raid6: add missing vzeroupper to AVX2 code
>   raid6: add missing vzeroupper to AVX-512 code
>   crypto: x86/aria - add missing vzeroupper in AVX2 code
>   crypto: x86/aria - add missing vzeroupper in AVX-512 code
>   netfilter: nft_set_pipapo_avx2: add missing vzeroupper
> 
>  arch/x86/crypto/aria-aesni-avx2-asm_64.S  |  6 ++++++
>  arch/x86/crypto/aria-gfni-avx512-asm_64.S |  3 +++
>  lib/raid/raid6/x86/avx2.c                 |  6 ++++++
>  lib/raid/raid6/x86/avx512.c               |  6 ++++++
>  lib/raid/raid6/x86/recov_avx2.c           |  2 ++
>  lib/raid/raid6/x86/recov_avx512.c         |  2 ++
>  lib/raid/xor/x86/xor-avx.c                |  1 +
>  net/netfilter/nft_set_pipapo_avx2.c       | 17 ++++++++---------
>  8 files changed, 34 insertions(+), 9 deletions(-)
> 
> 
> base-commit: db2ddb87143519e20a95aa36c60b36107b736a58