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From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Wed, 17 Aug 2016 14:35:46 -0700
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Subject: Re: RFC: Petition Intel/AMD to add POPF_IF insn
To: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Andy Lutomirski <luto@amacapital.net>, Sara Sharon <sara.sharon@intel.com>,
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On Wed, Aug 17, 2016 at 2:26 PM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> Of course, if somebody uses native_restore_fl() to actually *disable*
> interrupts (when they weren't already disabled), then this untested
> patch will just not work. But why would you do somethign so stupid?
> Famous last words...

Looking around, the vsmp code actually uses "native_restore_fl()" to
not just set the interrupt flag, but AC as well.

And the PV spinlock case has that "push;popf" sequence encoded in an alternate.

So that trivial patch may (or may not - still not tested) work for
some quick testing, but needs more effort for any *real* use.

                  Linus