linux-kernel - Re: [PATCH] release kvmclock page on reset

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Date:	Fri, 28 Jan 2011 22:09:28 +0100
From:	Jan Kiszka <jan.kiszka@....de>
To:	Glauber Costa <glommer@...hat.com>
CC:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	aliguori@...ibm.com
Subject: Re: [PATCH] release kvmclock page on reset

On 2011-01-28 20:48, Glauber Costa wrote:
> Up to know, we were relying on guest cooperation to turn off kvmclock.
> I just realized that even though this is fine and nice, a more robust
> method is to (also) turn it off on vcpu_reset on the hypervisor side.
> This will protect us against reboots, and we don't expect the guest
> to reset its cpu during normal operation anyway.
> 
> Signed-off-by: Glauber Costa <glommer@...hat.com>
> ---
>  arch/x86/kvm/x86.c |    5 +++++
>  1 files changed, 5 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index bcc0efc..38b55b3 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -5878,6 +5878,11 @@ int kvm_arch_vcpu_reset(struct kvm_vcpu *vcpu)
>  	kvm_make_request(KVM_REQ_EVENT, vcpu);
>  	vcpu->arch.apf.msr_val = 0;
>  
> +	if (vcpu->arch.time_page) {
> +		kvm_release_page_dirty(vcpu->arch.time_page);
> +		vcpu->arch.time_page = NULL;
> +	}
> +

kvm_arch_vcpu_reset is only called on vcpu setup and when it receives a
sipi (provided in-kernel irqchip is in use). If you want this page to be
consistently reset on guest reboot, you have to trigger this from user
space. But I thought we are doing this already in qemu, don't we?

Jan


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