From mboxrd@z Thu Jan  1 00:00:00 1970
From: Avi Kivity <avi@qumranet.com>
Subject: Re: [PATCH] virtio-balloon: do not attempt to release
 more	than available pages
Date: Wed, 05 Mar 2008 18:59:10 +0200
Message-ID: <47CED15E.4090504@qumranet.com>
References: <20080305162832.GA11563@dmt>
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Cc: kvm-devel <kvm-devel@lists.sourceforge.net>
To: Marcelo Tosatti <marcelo@kvack.org>
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Marcelo Tosatti wrote:
> Handle the case where the balloon target is larger than total ram size.
>
> BUG: unable to handle kernel paging request at 0000000000100100
> IP: [<ffffffff881970f9>] :virtio_balloon:leak__balloon+0x2e/0xbe
>
> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
>
> Index: virtio/virtio_balloon.c
> ===================================================================
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -122,10 +122,21 @@ static void release_pages_by_pfn(const u
>  	}
>  }
>  
> +static void update_target_size(struct virtio_balloon *vb)
> +{
> +	__le32 num_pages = cpu_to_le32(vb->num_pages);
> +
> +	vb->vdev->config->set(vb->vdev,
> +			      offsetof(struct virtio_balloon_config, num_pages),
> +			      &num_pages, sizeof(num_pages));
> +}
>   

The target is host-owned; moreover the problem may be temporary, but 
you've changed the target permanently.

Suggest sending the host a message (like the page list) indicating it 
couldn't allocate any more.

Also, we may have driven the guest close to oom with this.  We need to 
notify the host when the guest gets into a low-memory cannot swap condition.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.


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