linux-kernel - Re: RFC: Petition Intel/AMD to add POPF

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Message-ID: <f91d4c19-688b-ff13-8905-377c0f5cea77@redhat.com>
Date:   Fri, 19 Aug 2016 12:54:39 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Denys Vlasenko <dvlasenk@...hat.com>
Cc:     Andy Lutomirski <luto@...capital.net>,
        Sara Sharon <sara.sharon@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Christian König <christian.koenig@....com>,
        Vinod Koul <vinod.koul@...el.com>,
        Alex Deucher <alexander.deucher@....com>,
        Johannes Berg <johannes.berg@...el.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Andy Lutomirski <luto@...nel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Adrian Hunter <adrian.hunter@...el.com>
Subject: Re: RFC: Petition Intel/AMD to add POPF_IF insn



On 18/08/2016 19:24, Linus Torvalds wrote:
>> > I didn't do CPL0 tests yet. Realized that cli/sti can be tested in userspace
>> > if we set iopl(3) first.
> Yes, but it might not be the same. So the timings could be very
> different from a cpl0 case.

FWIW I recently measured around 20 cycles for a popf as well on
Haswell-EP and CPL=0 (that was for commit f2485b3e0c6c, "KVM: x86: use
guest_exit_irqoff", 2016-07-01).

Paolo