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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: aca6ff29c4
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
David Matlack 2016-03-08 16:19:44 -08:00 committed by Paolo Bonzini
parent 9522b37f5a
commit 313f636d5c
1 changed files with 3 additions and 0 deletions
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3
virt/kvm/kvm_main.c
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@ -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);
}