From: David Matlack <dmatlack@google.com>
Date: Wed, 9 Mar 2016 00:19:44 +0000 (-0800)
Subject: kvm: cap halt polling at exactly halt_poll_ns
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=313f636d5c490c9741d3f750dc8da33029edbc6b;p=linux.git

kvm: cap halt polling at exactly halt_poll_ns

When growing halt-polling, there is no check that the poll time exceeds
the limit. It's possible for vcpu->halt_poll_ns grow once past
halt_poll_ns, and stay there until a halt which takes longer than
vcpu->halt_poll_ns. For example, booting a Linux guest with
halt_poll_ns=11000:

 ... kvm:kvm_halt_poll_ns: vcpu 0: halt_poll_ns 0 (shrink 10000)
 ... kvm:kvm_halt_poll_ns: vcpu 0: halt_poll_ns 10000 (grow 0)
 ... kvm:kvm_halt_poll_ns: vcpu 0: halt_poll_ns 20000 (grow 10000)

Signed-off-by: David Matlack <dmatlack@google.com>
Fixes: aca6ff29c4063a8d467cdee241e6b3bf7dc4a171
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index a11cfd20a6a0d..9102ae172d2a9 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1952,6 +1952,9 @@ static void grow_halt_poll_ns(struct kvm_vcpu *vcpu)
 	else
 		val *= halt_poll_ns_grow;
 
+	if (val > halt_poll_ns)
+		val = halt_poll_ns;
+
 	vcpu->halt_poll_ns = val;
 	trace_kvm_halt_poll_ns_grow(vcpu->vcpu_id, val, old);
 }