[PATCH v2 3/9] arm64: fpsimd: run kernel mode NEON with softirqs disabled

[Will Deacon]

On Tue, Mar 02, 2021 at 10:01:12AM +0100, Ard Biesheuvel wrote:
> Kernel mode NEON can be used in task or softirq context, but only in
> a non-nesting manner, i.e., softirq context is only permitted if the
> interrupt was not taken at a point where the kernel was using the NEON
> in task context.
> 
> This means all users of kernel mode NEON have to be aware of this
> limitation, and either need to provide scalar fallbacks that may be much
> slower (up to 20x for AES instructions) and potentially less safe, or
> use an asynchronous interface that defers processing to a later time
> when the NEON is guaranteed to be available.
> 
> Given that grabbing and releasing the NEON is cheap, we can relax this
> restriction, by increasing the granularity of kernel mode NEON code, and
> always disabling softirq processing while the NEON is being used in task
> context.
> 
> Signed-off-by: Ard Biesheuvel <ardb at kernel.org>
> ---
>  arch/arm64/crypto/aes-modes.S      |  2 +-
>  arch/arm64/crypto/sha1-ce-core.S   |  2 +-
>  arch/arm64/crypto/sha2-ce-core.S   |  2 +-
>  arch/arm64/crypto/sha3-ce-core.S   |  4 +--
>  arch/arm64/crypto/sha512-ce-core.S |  2 +-
>  arch/arm64/include/asm/assembler.h | 28 +++++++++++++++-----
>  arch/arm64/kernel/asm-offsets.c    |  2 ++
>  arch/arm64/kernel/fpsimd.c         |  4 +--
>  8 files changed, 31 insertions(+), 15 deletions(-)

Acked-by: Will Deacon <will at kernel.org>

Will