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Date: Thu, 31 Jul 2014 18:44:00 +0100 From: Will Deacon <will.deacon@....com> To: Peter Maydell <peter.maydell@...aro.org> Cc: Paolo Bonzini <pbonzini@...hat.com>, Alex Bennée <alex.bennee@...aro.org>, "kvmarm@...ts.cs.columbia.edu" <kvmarm@...ts.cs.columbia.edu>, arm-mail-list <linux-arm-kernel@...ts.infradead.org>, kvm-devel <kvm@...r.kernel.org>, Catalin Marinas <Catalin.Marinas@....com>, open list <linux-kernel@...r.kernel.org>, Gleb Natapov <gleb@...nel.org> Subject: Re: [PATCH] arm64: KVM: export current vcpu->pause state via pseudo regs On Thu, Jul 31, 2014 at 06:36:35PM +0100, Peter Maydell wrote: > On 31 July 2014 18:21, Paolo Bonzini <pbonzini@...hat.com> wrote: > > What does ARM do if you have a WFI while interrupts are disabled? On > > x86 after "cli;hlt" only an NMI will wake you up. With spurious > > wakeups, it's pretty much guaranteed that you will break such "cli;hlt" > > sequences. > > The architecture mandates some things that *must* wake you from > a WFI, but it also allows wakeups for other reasons not listed, or > for no reason at all. It's perfectly valid to implement WFI as a NOP > (though it would not be very good for power efficiency, obviously). > Guests which don't surround WFI with a "check whether we should > just go back to WFI" loop are buggy. (and in case that wasn't clear, local_irq_disable() doesn't prevent an interrupt from waking you up from wfi, otherwise our idle code would be broken). Will -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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