Hi,

On 14/02/2019 10:34, Dave Martin wrote:

On Wed, Feb 13, 2019 at 05:52:27PM +0100, Sebastian Andrzej Siewior wrote:

quoted

On 2019-02-13 16:40:00 [+0100], Ard Biesheuvel wrote:

quoted

quoted

quoted

This is equal what x86 is currently doing. The naming is slightly
different, there is irq_fpu_usable().

Yes, I think it's basically the same idea.

It's been evolving a bit on both sides, but is quite similar now.

may_use_simd() only exists because we have a generic crypto SIMD
helper, and so we needed something arch agnostic to wrap around
irq_fpu_usable()

My question was more if this is helpful and we want to keep or if
it would be better to remove it and always disable BH as part of SIMD
operations.

Wouldn't this arbitrarily increase softirq latency?  Unconditionally
forbidding SIMD in softirq might make more sense.  It depends on how
important the use cases are...

Looking at the commit message from cb84d11e1625 "arm64: neon: Remove support for 
nested or hardirq kernel-mode NEON", one of the use case for crypto in softirq 
is certain mac80211 drivers.

Is there any other use case for use crypto in softirqs?

Cheers,

-- 
Julien Grall

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