KVM: Fix race between timer migration and vcpu migration (d4acf7e7) · Commits · 戴 / test

A guest vcpu instance can be scheduled to a different physical CPU between the test for KVM_REQ_MIGRATE_TIMER and local_irq_disable(). If that happens, the timer will only be migrated to the current pCPU on the next exit, meaning that guest LAPIC timer event can be delayed until a host interrupt is triggered. Fix it by cancelling guest entry if any vcpu request is pending. This has the side effect of nicely consolidating vcpu->requests checks. Signed-off-by:

Marcelo Tosatti <mtosatti@redhat.com> Signed-off-by:

Avi Kivity <avi@qumranet.com>

arch/x86/kvm/x86.c

+3 −12

Original line number	Diff line number	Diff line
		@@ -2759,6 +2759,8 @@ again:
		if (vcpu->requests) {
		if (test_and_clear_bit(KVM_REQ_MIGRATE_TIMER, &vcpu->requests))
		__kvm_migrate_timers(vcpu);
		if (test_and_clear_bit(KVM_REQ_TLB_FLUSH, &vcpu->requests))
		kvm_x86_ops->tlb_flush(vcpu);
		if (test_and_clear_bit(KVM_REQ_REPORT_TPR_ACCESS,
		&vcpu->requests)) {
		kvm_run->exit_reason = KVM_EXIT_TPR_ACCESS;
		@@ -2781,15 +2783,7 @@ again:

		local_irq_disable();

		if (need_resched()) {
		local_irq_enable();
		preempt_enable();
		r = 1;
		goto out;
		}

		if (vcpu->requests)
		if (test_bit(KVM_REQ_MMU_RELOAD, &vcpu->requests)) {
		if (vcpu->requests \|\| need_resched()) {
		local_irq_enable();
		preempt_enable();
		r = 1;
		@@ -2825,9 +2819,6 @@ again:

		kvm_guest_enter();

		if (vcpu->requests)
		if (test_and_clear_bit(KVM_REQ_TLB_FLUSH, &vcpu->requests))
		kvm_x86_ops->tlb_flush(vcpu);

		KVMTRACE_0D(VMENTRY, vcpu, entryexit);
		kvm_x86_ops->run(vcpu, kvm_run);

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