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>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 4de705cdcafd33d025083e62d6d56b323342bdc2..b78f89d34242c249842479fd946360e0cc91d462 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -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);