linux-kernel - Re: [RFC PATCH v2 6/7] KVM: fix the race while wakeup all pv guest

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Date:	Mon, 1 Nov 2010 14:58:05 +0200
From:	Gleb Natapov <gleb@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
Cc:	Avi Kivity <avi@...hat.com>, Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [RFC PATCH v2 6/7] KVM: fix the race while wakeup all pv guest

On Mon, Nov 01, 2010 at 05:03:44PM +0800, Xiao Guangrong wrote:
> In kvm_async_pf_wakeup_all(), we add a dummy apf to vcpu->async_pf.done
> without holding vcpu->async_pf.lock, it will break if we are handling apfs
> at this time.
> 
This should never happen to well behaved guest, but malicious guest can do it
on purpose.

> Also use 'list_empty_careful()' instead of 'list_empty()'
> 
> Signed-off-by: Xiao Guangrong <xiaoguangrong@...fujitsu.com>
Acked-by: Gleb Natapov <gleb@...hat.com>

> ---
>  virt/kvm/async_pf.c |    5 ++++-
>  1 files changed, 4 insertions(+), 1 deletions(-)
> 
> diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c
> index d57ec92..6ef3373 100644
> --- a/virt/kvm/async_pf.c
> +++ b/virt/kvm/async_pf.c
> @@ -200,7 +200,7 @@ int kvm_async_pf_wakeup_all(struct kvm_vcpu *vcpu)
>  {
>  	struct kvm_async_pf *work;
>  
> -	if (!list_empty(&vcpu->async_pf.done))
> +	if (!list_empty_careful(&vcpu->async_pf.done))
>  		return 0;
>  
>  	work = kmem_cache_zalloc(async_pf_cache, GFP_ATOMIC);
> @@ -211,7 +211,10 @@ int kvm_async_pf_wakeup_all(struct kvm_vcpu *vcpu)
>  	get_page(bad_page);
>  	INIT_LIST_HEAD(&work->queue); /* for list_del to work */
>  
> +	spin_lock(&vcpu->async_pf.lock);
>  	list_add_tail(&work->link, &vcpu->async_pf.done);
> +	spin_unlock(&vcpu->async_pf.lock);
> +
>  	vcpu->async_pf.queued++;
>  	return 0;
>  }
> -- 
> 1.7.0.4

--
			Gleb.
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