From: will.deacon@arm.com (Will Deacon)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH] arm64: KVM: export current vcpu->pause state via pseudo regs
Date: Thu, 31 Jul 2014 18:44:00 +0100 [thread overview]
Message-ID: <20140731174359.GI26853@arm.com> (raw)
In-Reply-To: <CAFEAcA8RjmjoaEpjoDE5YJdKagtZYZe9TpCdsRPf86W=WCxCsA@mail.gmail.com>
On Thu, Jul 31, 2014 at 06:36:35PM +0100, Peter Maydell wrote:
> On 31 July 2014 18:21, Paolo Bonzini <pbonzini@redhat.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
WARNING: multiple messages have this Message-ID (diff)
From: Will Deacon <will.deacon@arm.com>
To: Peter Maydell <peter.maydell@linaro.org>
Cc: "Paolo Bonzini" <pbonzini@redhat.com>,
"Alex Bennée" <alex.bennee@linaro.org>,
"kvmarm@lists.cs.columbia.edu" <kvmarm@lists.cs.columbia.edu>,
arm-mail-list <linux-arm-kernel@lists.infradead.org>,
kvm-devel <kvm@vger.kernel.org>,
"Catalin Marinas" <Catalin.Marinas@arm.com>,
"open list" <linux-kernel@vger.kernel.org>,
"Gleb Natapov" <gleb@kernel.org>
Subject: Re: [PATCH] arm64: KVM: export current vcpu->pause state via pseudo regs
Date: Thu, 31 Jul 2014 18:44:00 +0100 [thread overview]
Message-ID: <20140731174359.GI26853@arm.com> (raw)
In-Reply-To: <CAFEAcA8RjmjoaEpjoDE5YJdKagtZYZe9TpCdsRPf86W=WCxCsA@mail.gmail.com>
On Thu, Jul 31, 2014 at 06:36:35PM +0100, Peter Maydell wrote:
> On 31 July 2014 18:21, Paolo Bonzini <pbonzini@redhat.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
next prev parent reply other threads:[~2014-07-31 17:44 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-07-09 13:55 [PATCH] arm64: KVM: export current vcpu->pause state via pseudo regs Alex Bennée
2014-07-09 13:55 ` Alex Bennée
2014-07-31 14:35 ` Christoffer Dall
2014-07-31 14:35 ` Christoffer Dall
2014-07-31 15:14 ` Alex Bennée
2014-07-31 15:14 ` Alex Bennée
2014-07-31 16:38 ` Christoffer Dall
2014-07-31 16:38 ` Christoffer Dall
2014-07-31 16:45 ` Peter Maydell
2014-07-31 16:45 ` Peter Maydell
2014-07-31 16:50 ` Christoffer Dall
2014-07-31 16:50 ` Christoffer Dall
2014-07-31 16:53 ` Peter Maydell
2014-07-31 16:53 ` Peter Maydell
2014-08-01 9:48 ` Alex Bennée
2014-08-01 9:48 ` Alex Bennée
2014-08-04 12:11 ` Christoffer Dall
2014-08-04 12:11 ` Christoffer Dall
2014-08-01 9:11 ` Alex Bennée
2014-08-01 9:11 ` Alex Bennée
2014-08-04 12:13 ` Christoffer Dall
2014-08-04 12:13 ` Christoffer Dall
2014-07-31 16:57 ` Paolo Bonzini
2014-07-31 16:57 ` Paolo Bonzini
2014-07-31 17:04 ` Peter Maydell
2014-07-31 17:04 ` Peter Maydell
2014-07-31 17:21 ` Paolo Bonzini
2014-07-31 17:21 ` Paolo Bonzini
2014-07-31 17:36 ` Peter Maydell
2014-07-31 17:36 ` Peter Maydell
2014-07-31 17:44 ` Will Deacon [this message]
2014-07-31 17:44 ` Will Deacon
2014-08-04 12:16 ` Christoffer Dall
2014-08-04 12:16 ` Christoffer Dall
2014-08-04 12:35 ` Alex Bennée
2014-08-04 12:35 ` Alex Bennée
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