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Message-ID: <4D4FD8EE.6040009@siemens.com> Date: Mon, 07 Feb 2011 12:35:10 +0100 From: Jan Kiszka <jan.kiszka@...mens.com> To: Zachary Amsden <zamsden@...hat.com> CC: Avi Kivity <avi@...hat.com>, Marcelo Tosatti <mtosatti@...hat.com>, kvm <kvm@...r.kernel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: Re: [PATCH] KVM: x86: Convert tsc_write_lock to raw_spinlock On 2011-02-04 22:03, Zachary Amsden wrote: > On 02/04/2011 04:49 AM, Jan Kiszka wrote: >> Code under this lock requires non-preemptibility. Ensure this also over >> -rt by converting it to raw spinlock. >> > > Oh dear, I had forgotten about that. I believe kvm_lock might have the > same assumption in a few places regarding clock. I only found a problematic section in kvmclock_cpufreq_notifier. Didn't see this during my tests as I have CPUFREQ disabled in my .config. We may need something like this as converting kvm_lock would likely be overkill: diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 36f54fb..971ee0d 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -4530,7 +4530,7 @@ static int kvmclock_cpufreq_notifier(struct notifier_block *nb, unsigned long va struct cpufreq_freqs *freq = data; struct kvm *kvm; struct kvm_vcpu *vcpu; - int i, send_ipi = 0; + int i, me, send_ipi = 0; /* * We allow guests to temporarily run on slowing clocks, @@ -4583,9 +4583,11 @@ static int kvmclock_cpufreq_notifier(struct notifier_block *nb, unsigned long va kvm_for_each_vcpu(i, vcpu, kvm) { if (vcpu->cpu != freq->cpu) continue; + me = get_cpu(); kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu); - if (vcpu->cpu != smp_processor_id()) + if (vcpu->cpu != me) send_ipi = 1; + put_cpu(); } } spin_unlock(&kvm_lock); Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux -- 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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