From: Andy Lutomirski <luto@amacapital.net>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "Denys Vlasenko" <dvlasenk@redhat.com>,
"Sara Sharon" <sara.sharon@intel.com>,
"Dan Williams" <dan.j.williams@intel.com>,
"Christian König" <christian.koenig@amd.com>,
"Vinod Koul" <vinod.koul@intel.com>,
"Alex Deucher" <alexander.deucher@amd.com>,
"Johannes Berg" <johannes.berg@intel.com>,
"Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
"Andy Lutomirski" <luto@kernel.org>,
"the arch/x86 maintainers" <x86@kernel.org>,
"Ingo Molnar" <mingo@kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
"Adrian Hunter" <adrian.hunter@intel.com>
Subject: Re: RFC: Petition Intel/AMD to add POPF_IF insn
Date: Wed, 17 Aug 2016 14:43:27 -0700 [thread overview]
Message-ID: <CALCETrXZpbzF=HUVNvOZjhF+DGYA1viYdDa_aaBVHJVQb=6eGA@mail.gmail.com> (raw)
In-Reply-To: <CA+55aFyf9UAhQp48YCtqNnvSs_tC3W51uCb00nMND7ZG8KQexA@mail.gmail.com>
On Wed, Aug 17, 2016 at 2:35 PM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
> 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.
>
It shouldn't be *too* bad, since xen_restore_fl only affects "IF".
And even if native_restore_fl needs to be able to turn IRQs off as
well as on, we can just do:
if (likely(flags & X86_EFLAGS_IF))
sti();
else
cli();
at some cost to code size but hopefully little to no runtime cost for
the sane cases.
next prev parent reply other threads:[~2016-08-17 21:43 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-17 17:20 RFC: Petition Intel/AMD to add POPF_IF insn Denys Vlasenko
2016-08-17 17:30 ` Christian König
2016-08-17 18:34 ` Denys Vlasenko
2016-08-17 17:32 ` Linus Torvalds
2016-08-17 18:41 ` Denys Vlasenko
[not found] ` <CA+55aFwmxwQBkyDjombS4cy1q=a_buhmDjDnaa8rdC8ZDaDYEA@mail.gmail.com>
2016-08-17 19:13 ` Andy Lutomirski
2016-08-17 19:26 ` Denys Vlasenko
2016-08-17 19:32 ` Linus Torvalds
2016-08-17 19:35 ` Denys Vlasenko
2016-08-17 19:54 ` Linus Torvalds
2016-08-17 19:37 ` Linus Torvalds
2016-08-17 21:26 ` Linus Torvalds
2016-08-17 21:35 ` Linus Torvalds
2016-08-17 21:43 ` Andy Lutomirski [this message]
2016-08-17 21:48 ` Linus Torvalds
2016-08-18 13:26 ` Denys Vlasenko
2016-08-18 17:24 ` Linus Torvalds
2016-08-18 17:47 ` Denys Vlasenko
2016-08-18 17:49 ` Denys Vlasenko
2016-08-19 10:54 ` Paolo Bonzini
2016-08-31 11:12 ` Denys Vlasenko
2016-08-18 9:21 ` Denys Vlasenko
2016-08-18 12:18 ` Denys Vlasenko
2016-08-18 17:22 ` Paolo Bonzini
2016-08-17 19:29 ` Linus Torvalds
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