kvm: x86: Use fast CR3 switch for nested VMX

Use the fast CR3 switch mechanism to locklessly change the MMU root
page when switching between L1 and L2. The switch from L2 to L1 should
always go through the fast path, while the switch from L1 to L2 should
go through the fast path if L1's CR3/EPTP for L2 hasn't changed
since the last time.

Signed-off-by: Junaid Shahid <junaids@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 10 insertions, 4 deletions

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index f519eb8d06b1..8f461e0ed382 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2127,16 +2127,22 @@ static void shrink_halt_poll_ns(struct kvm_vcpu *vcpu)
 
 static int kvm_vcpu_check_block(struct kvm_vcpu *vcpu)
 {
+        int ret = -EINTR;
+        int idx = srcu_read_lock(&vcpu->kvm->srcu);
+
         if (kvm_arch_vcpu_runnable(vcpu)) {
                 kvm_make_request(KVM_REQ_UNHALT, vcpu);
-                return -EINTR;
+                goto out;
         }
         if (kvm_cpu_has_pending_timer(vcpu))
-                return -EINTR;
+                goto out;
         if (signal_pending(current))
-                return -EINTR;
+                goto out;
 
-        return 0;
+        ret = 0;
+out:
+        srcu_read_unlock(&vcpu->kvm->srcu, idx);
+        return ret;
 }
 
 /*