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

On Sat, 15 Aug 2026 13:57:44 -0700
Eric Biggers [off-list ref] 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