Re: [patch 00/13] preempt: Make preempt count unconditional

On Tue, Sep 15, 2020 at 09:20:59AM +0300, Ard Biesheuvel wrote:

The documentation of kmap_atomic() states the following:

• The use of kmap_atomic/kunmap_atomic is discouraged - kmap/kunmap
• gives a more generic (and caching) interface. But kmap_atomic can
• be used in IRQ contexts, so in some (very limited) cases we need
• it.

so if this is no longer accurate, perhaps we should fix it?

This hasn't been accurate for at least ten years :)

But another reason I tried to avoid kmap_atomic() is that it disables preemption unconditionally, even on 64-bit architectures where HIGHMEM is irrelevant. So using kmap_atomic() here means that the bulk of WireGuard packet encryption runs with preemption disabled, essentially for legacy reasons.

Agreed. We should definitely fix that.

Thanks,