kvm: Cap halt polling at kvm->max_halt_poll_ns

When growing halt-polling, there is no check that the poll time exceeds
the per-VM limit. It's possible for vcpu->halt_poll_ns to grow past
kvm->max_halt_poll_ns and stay there until a halt which takes longer
than kvm->halt_poll_ns.

Signed-off-by: David Matlack <dmatlack@google.com>
Signed-off-by: Venkatesh Srinivas <venkateshs@chromium.org>
Message-Id: <20210506152442.4010298-1-venkateshs@chromium.org>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Author: dmatlack

virt/kvm/kvm_main.c

@@ -2893,8 +2893,8 @@ static void grow_halt_poll_ns(struct kvm_vcpu *vcpu)
 	if (val < grow_start)
 		val = grow_start;
 
-	if (val > halt_poll_ns)
-		val = halt_poll_ns;
+	if (val > vcpu->kvm->max_halt_poll_ns)
+		val = vcpu->kvm->max_halt_poll_ns;
 
 	vcpu->halt_poll_ns = val;
 out: