Re: [PATCH crypto-stable] crypto: arch/lib - limit simd usage to PAGE_SIZE chunks

["Jason A. Donenfeld" <Jason@zx2c4.com>]

On Mon, Apr 20, 2020 at 2:32 AM David Laight <David.Laight@aculab.com> wrote:
> Maybe kernel_fp_begin() should be passed the address of somewhere
> the address of an fpu save area buffer can be written to.
> Then the pre-emption code can allocate the buffer and save the
> state into it.
>
> However that doesn't solve the problem for non-preemptive kernels.
> The may need a cond_resched() in the loop if it might take 1ms (or so).
>
> kernel_fpu_begin() ought also be passed a parameter saying which
> fpu features are required, and return which are allocated.
> On x86 this could be used to check for AVX512 (etc) which may be
> available in an ISR unless it interrupted inside a kernel_fpu_begin()
> section (etc).
> It would also allow optimisations if only 1 or 2 fpu registers are
> needed (eg for some of the crypto functions) rather than the whole
> fpu register set.

There might be ways to improve lots of FPU things, indeed. This patch
here is just a patch to Herbert's branch in order to make uniform
usage of our existing solution for this, fixing the existing bug. I
wouldn't mind seeing more involved and better solutions in a patchset
for crypto-next.

Will follow up with your suggestion in a different thread, so as not
to block this one.