On 24.04.20 18:24, Alexander Duyck wrote:
> From: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>
>
> We should disable free page reporting if page poisoning is enabled in the
> kernel but we cannot report it via the balloon interface. This way we can
> avoid the possibility of corrupting guest memory. Normally the page poison
> reporting feature should always be present when free page reporting is
> enabled on the hypervisor, however this allows us to correctly handle a
> case of the virtio-balloon device being possibly misconfigured.
>
> Fixes: 5d757c8d518d ("virtio-balloon: add support for providing free page reports to host")
> Signed-off-by: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>
> ---
>
> Changes since v1:
> Originally this patch also modified free page hinting, that has been removed.
> Updated patch title and description.
> Added a comment explaining reasoning for disabling free page reporting.
>
> drivers/virtio/virtio_balloon.c | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index 51086a5afdd4..1f157d2f4952 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -1107,11 +1107,18 @@ static int virtballoon_restore(struct virtio_device *vdev)
>
> static int virtballoon_validate(struct virtio_device *vdev)
> {
> - /* Tell the host whether we care about poisoned pages. */
> + /*
> + * Inform the hypervisor that our pages are poisoned or
> + * initialized. If we cannot do that then we should disable
> + * page reporting as it could potentially change the contents
> + * of our free pages.
> + */
> if (!want_init_on_free() &&
> (IS_ENABLED(CONFIG_PAGE_POISONING_NO_SANITY) ||
> !page_poisoning_enabled()))
> __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_PAGE_POISON);
> + else if (!virtio_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_POISON))
> + __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_REPORTING);
>
> __virtio_clear_bit(vdev, VIRTIO_F_IOMMU_PLATFORM);
> return 0;
>
Did you see my feedback on v1?
https://www.spinics.net/lists/linux-virtualization/msg42783.html
In case of want_init_on_free(), we don't really need VIRTIO_BALLOON_F_PAGE_POISON.
--
Thanks,
David / dhildenb
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