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SubjectRe: [PATCH] crypto: lib/chacha20poly1305 - Set SG_MITER_ATOMIC unconditionally
On Mon, Sep 14, 2020 at 11:55:53PM -0700, Linus Torvalds wrote:
> Maybe we could hide it behind a debug option, at least.
> Or, alterantively, introduce a new "debug_preempt_count" that doesn't
> actually disable preemption, but warns about actual sleeping
> operations..

I'm more worried about existing users of kmap_atomic relying on
the preemption disabling semantics. Short of someone checking
on every single instance (and that would include derived cases
such as all users of sg miter), I think the safer option is to
create something brand new and then migrate the existing users
to it. Something like

static inline void *kmap_atomic_ifhigh(struct page *page)
if (PageHighMem(page))
return kmap_atomic(page);
return page_address(page);

static inline void kunmap_atomic_ifhigh(struct page *page, void *addr)
if (PageHighMem(page))

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