Commit d8368af8 authored May 14, 2012 by Avi Kivity Committed by Marcelo Tosatti May 16, 2012

KVM: Fix mmu_reload() clash with nested vmx event injection

Currently the inject_pending_event() call during guest entry happens after
kvm_mmu_reload().  This is for historical reasons - we used to
inject_pending_event() in atomic context, while kvm_mmu_reload() needs task
context.

A problem is that nested vmx can cause the mmu context to be reset, if event
injection is intercepted and causes a #VMEXIT instead (the #VMEXIT resets
CR0/CR3/CR4).  If this happens, we end up with invalid root_hpa, and since
kvm_mmu_reload() has already run, no one will fix it and we end up entering
the guest this way.

Fix by reordering event injection to be before kvm_mmu_reload().  Use
->cancel_injection() to undo if kvm_mmu_reload() fails.

https://bugzilla.kernel.org/show_bug.cgi?id=42980



Reported-by: Luke-Jr <luke-jr+linuxbugs@utopios.org>
Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

parent c142786c

arch/x86/kvm/x86.c

+6 −4

Original line number	Diff line number	Diff line
		@@ -5279,10 +5279,6 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
		kvm_deliver_pmi(vcpu);
		}

		r = kvm_mmu_reload(vcpu);
		if (unlikely(r))
		goto out;

		if (kvm_check_request(KVM_REQ_EVENT, vcpu) \|\| req_int_win) {
		inject_pending_event(vcpu);

		@@ -5298,6 +5294,12 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
		}
		}

		r = kvm_mmu_reload(vcpu);
		if (unlikely(r)) {
		kvm_x86_ops->cancel_injection(vcpu);
		goto out;
		}

		preempt_disable();

		kvm_x86_ops->prepare_guest_switch(vcpu);