[Devel] [PATCH RHEL7 COMMIT] ms/kvm: cap halt polling at exactly halt_poll_ns

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-327.10.1.vz7.12.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-327.10.1.vz7.12.11
------>
commit d234f475baa2cc3bfdf80265734a0b52439b347f
Author: David Matlack <dmatlack at google.com>
Date:   Tue Apr 19 14:22:52 2016 +0400

    ms/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 at google.com>
    Fixes: aca6ff29c4063a8d467cdee241e6b3bf7dc4a171
    Cc: stable at vger.kernel.org
    Signed-off-by: Paolo Bonzini <pbonzini at redhat.com>
    (cherry picked from commit 313f636d5c490c9741d3f750dc8da33029edbc6b)
    
    Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov at virtuozzo.com>
---
 virt/kvm/kvm_main.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 4cbac86..1aa2217 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1955,6 +1955,9 @@ static void grow_halt_poll_ns(struct kvm_vcpu *vcpu)
 	else
 		val *= 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);
 }