KVM: x86: disable preemption around the call to kvm_arch_vcpu_{un|}blocking

On SVM, if preemption happens right after the call to finish_rcuwait
but before call to kvm_arch_vcpu_unblocking on SVM/AVIC, it itself
will re-enable AVIC, and then we will try to re-enable it again
in kvm_arch_vcpu_unblocking which will lead to a warning
in __avic_vcpu_load.

The same problem can happen if the vCPU is preempted right after the call
to kvm_arch_vcpu_blocking but before the call to prepare_to_rcuwait
and in this case, we will end up with AVIC enabled during sleep -
Ooops.

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20220606180829.102503-7-mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 44c4767..a49df89 100644 (file)
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -3328,9 +3328,11 @@ bool kvm_vcpu_block(struct kvm_vcpu *vcpu)
 
        vcpu->stat.generic.blocking = 1;
 
+       preempt_disable();
        kvm_arch_vcpu_blocking(vcpu);
-
        prepare_to_rcuwait(wait);
+       preempt_enable();
+
        for (;;) {
                set_current_state(TASK_INTERRUPTIBLE);
 
@@ -3340,9 +3342,11 @@ bool kvm_vcpu_block(struct kvm_vcpu *vcpu)
                waited = true;
                schedule();
        }
-       finish_rcuwait(wait);
 
+       preempt_disable();
+       finish_rcuwait(wait);
        kvm_arch_vcpu_unblocking(vcpu);
+       preempt_enable();
 
        vcpu->stat.generic.blocking = 0;