Commit 9242b5b6 authored Jul 08, 2014 by Bandan Das Committed by Paolo Bonzini Jul 08, 2014

KVM: x86: Check for nested events if there is an injectable interrupt



With commit b6b8a145 that introduced
vmx_check_nested_events, checks for injectable interrupts happen
at different points in time for L1 and L2 that could potentially
cause a race. The regression occurs because KVM_REQ_EVENT is always
set when nested_run_pending is set even if there's no pending interrupt.
Consequently, there could be a small window when check_nested_events
returns without exiting to L1, but an interrupt comes through soon
after and it incorrectly, gets injected to L2 by inject_pending_event
Fix this by adding a call to check for nested events too when a check
for injectable interrupt returns true

Signed-off-by: Bandan Das <bsd@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

parent cd3de83f

arch/x86/kvm/x86.c

+12 −0

Original line number	Diff line number	Diff line
		@@ -5887,6 +5887,18 @@ static int inject_pending_event(struct kvm_vcpu *vcpu, bool req_int_win)
		kvm_x86_ops->set_nmi(vcpu);
		}
		} else if (kvm_cpu_has_injectable_intr(vcpu)) {
		/*
		* Because interrupts can be injected asynchronously, we are
		* calling check_nested_events again here to avoid a race condition.
		* See https://lkml.org/lkml/2014/7/2/60 for discussion about this
		* proposal and current concerns. Perhaps we should be setting
		* KVM_REQ_EVENT only on certain events and not unconditionally?
		*/
		if (is_guest_mode(vcpu) && kvm_x86_ops->check_nested_events) {
		r = kvm_x86_ops->check_nested_events(vcpu, req_int_win);
		if (r != 0)
		return r;
		}
		if (kvm_x86_ops->interrupt_allowed(vcpu)) {
		kvm_queue_interrupt(vcpu, kvm_cpu_get_interrupt(vcpu),
		false);

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