2016-03-09 00:20:04

by David Matlack

Subject: [PATCH] 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 <[email protected]>
---
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 a11cfd2..9102ae1 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);
}
--
2.7.0.rc3.207.g0ac5344

2016-03-09 10:55:32

by Paolo Bonzini

Subject: Re: [PATCH] kvm: cap halt polling at exactly halt_poll_ns

On 09/03/2016 01:19, David Matlack wrote:
> 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 <[email protected]>
> ---
> 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 a11cfd2..9102ae1 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);
> }
>

Applied to kvm/master, thanks.

Paolo