Subject: Re: [PATCH] kvm: cap halt polling at exactly halt_poll_ns
To: David Matlack <dmatlack@google.com>, kvm@vger.kernel.org
References: <1457482784-82531-1-git-send-email-dmatlack@google.com>
Cc: linux-kernel@vger.kernel.org, wanpeng.li@hotmail.com
From: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <56E00119.9060702@redhat.com>
Date: Wed, 9 Mar 2016 11:55:21 +0100
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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 <dmatlack@google.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 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