6.16-stable review patch. If anyone has any objections, please let me know.
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From: Eric Biggers ebiggers@kernel.org
commit 9f65592b7e1f24569bb6ced064df5b4319f725ce upstream.
Restore the len >= 288 condition on using the AVX implementation, which was incidentally removed by commit 318c53ae02f2 ("crypto: x86/poly1305 - Add block-only interface"). This check took into account the overhead in key power computation, kernel-mode "FPU", and tail handling associated with the AVX code. Indeed, restoring this check slightly improves performance for len < 256 as measured using poly1305_kunit on an "AMD Ryzen AI 9 365" (Zen 5) CPU:
Length Before After ====== ========== ========== 1 30 MB/s 36 MB/s 16 516 MB/s 598 MB/s 64 1700 MB/s 1882 MB/s 127 2265 MB/s 2651 MB/s 128 2457 MB/s 2827 MB/s 200 2702 MB/s 3238 MB/s 256 3841 MB/s 3768 MB/s 511 4580 MB/s 4585 MB/s 512 5430 MB/s 5398 MB/s 1024 7268 MB/s 7305 MB/s 3173 8999 MB/s 8948 MB/s 4096 9942 MB/s 9921 MB/s 16384 10557 MB/s 10545 MB/s
While the optimal threshold for this CPU might be slightly lower than 288 (see the len == 256 case), other CPUs would need to be tested too, and these sorts of benchmarks can underestimate the true cost of kernel-mode "FPU". Therefore, for now just restore the 288 threshold.
Fixes: 318c53ae02f2 ("crypto: x86/poly1305 - Add block-only interface") Cc: stable@vger.kernel.org Reviewed-by: Ard Biesheuvel ardb@kernel.org Link: https://lore.kernel.org/r/20250706231100.176113-6-ebiggers@kernel.org Signed-off-by: Eric Biggers ebiggers@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/lib/crypto/poly1305_glue.c | 8 ++++++++ 1 file changed, 8 insertions(+)
--- a/arch/x86/lib/crypto/poly1305_glue.c +++ b/arch/x86/lib/crypto/poly1305_glue.c @@ -98,7 +98,15 @@ void poly1305_blocks_arch(struct poly130 BUILD_BUG_ON(SZ_4K < POLY1305_BLOCK_SIZE || SZ_4K % POLY1305_BLOCK_SIZE);
+ /* + * The AVX implementations have significant setup overhead (e.g. key + * power computation, kernel FPU enabling) which makes them slower for + * short messages. Fall back to the scalar implementation for messages + * shorter than 288 bytes, unless the AVX-specific key setup has already + * been performed (indicated by ctx->is_base2_26). + */ if (!static_branch_likely(&poly1305_use_avx) || + (len < POLY1305_BLOCK_SIZE * 18 && !ctx->is_base2_26) || unlikely(!irq_fpu_usable())) { convert_to_base2_64(ctx); poly1305_blocks_x86_64(ctx, inp, len, padbit);