lib/crc: x86: Opt out of initializing MXCSR and 387 state

The CRC code using "kernel-mode FPU" is integer code that does not use
any MMX or x87 instructions.  To the extent that float-domain
instructions are used at all, they are only moves and shuffles, neither
of which raises SIMD floating-point exceptions or depends on MXCSR.

Therefore, there's no need to initialize MXCSR or the 387 FPU state.

Opt out of this initialization by using kernel_fpu_begin_mask(0) instead
of kernel_fpu_begin().  This eliminates an 'ldmxcsr' instruction in
every kernel-mode FPU section, reducing overhead, which matters most for
short input lengths.  On 32-bit kernels it also eliminates 'fninit'.

A precedent for this optimization can be found in
commit a58db7ad80e8 ("netfilter: nft_set_pipapo_avx2: Skip LDMXCSR, we
don't need a valid MXCSR state").

Link: https://patch.msgid.link/20261105005523.84925-2-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>

0 files changed, 0 insertions, 0 deletions