arm/arm64: KVM: Properly account for guest CPU time (1b3d546d) · Commits · 戴 / test

Until now we have been calling kvm_guest_exit after re-enabling interrupts when we come back from the guest, but this has the unfortunate effect that CPU time accounting done in the context of timer interrupts occurring while the guest is running doesn't properly notice that the time since the last tick was spent in the guest. Inspired by the comment in the x86 code, move the kvm_guest_exit() call below the local_irq_enable() call and change __kvm_guest_exit() to kvm_guest_exit(), because we are now calling this function with interrupts enabled. We have to now explicitly disable preemption and not enable preemption before we've called kvm_guest_exit(), since otherwise we could be preempted and everything happening before we eventually get scheduled again would be accounted for as guest time. At the same time, move the trace_kvm_exit() call outside of the atomic section, since there is no reason for us to do that with interrupts disabled. Signed-off-by:

Christoffer Dall <christoffer.dall@linaro.org> Signed-off-by:

Marc Zyngier <marc.zyngier@arm.com>

arch/arm/kvm/arm.c

+17 −4

Original line number	Diff line number	Diff line
		@@ -531,6 +531,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu vcpu, struct kvm_run run)
		kvm_vgic_flush_hwstate(vcpu);
		kvm_timer_flush_hwstate(vcpu);

		preempt_disable();
		local_irq_disable();

		/*
		@@ -543,6 +544,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu vcpu, struct kvm_run run)

		if (ret <= 0 \|\| need_new_vmid_gen(vcpu->kvm)) {
		local_irq_enable();
		preempt_enable();
		kvm_timer_sync_hwstate(vcpu);
		kvm_vgic_sync_hwstate(vcpu);
		continue;
		@@ -558,8 +560,10 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu vcpu, struct kvm_run run)
		ret = kvm_call_hyp(__kvm_vcpu_run, vcpu);

		vcpu->mode = OUTSIDE_GUEST_MODE;
		__kvm_guest_exit();
		trace_kvm_exit(kvm_vcpu_trap_get_class(vcpu), *vcpu_pc(vcpu));
		/*
		* Back from guest
		*************************************************************/

		/*
		* We may have taken a host interrupt in HYP mode (ie
		* while executing the guest). This interrupt is still
		@@ -573,8 +577,17 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu vcpu, struct kvm_run run)
		local_irq_enable();

		/*
		* Back from guest
		*************************************************************/
		* We do local_irq_enable() before calling kvm_guest_exit() so
		* that if a timer interrupt hits while running the guest we
		* account that tick as being spent in the guest. We enable
		* preemption after calling kvm_guest_exit() so that if we get
		* preempted we make sure ticks after that is not counted as
		* guest time.
		*/
		kvm_guest_exit();
		trace_kvm_exit(kvm_vcpu_trap_get_class(vcpu), *vcpu_pc(vcpu));
		preempt_enable();


		kvm_timer_sync_hwstate(vcpu);
		kvm_vgic_sync_hwstate(vcpu);

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