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SubjectRe: [PATCH v37 0/3] Virtio-balloon: support free page reporting
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On 27.12.2018 12:59, Christian Borntraeger wrote:
> On 27.12.2018 12:31, Christian Borntraeger wrote:
>> This patch triggers random crashes in the guest kernel on s390 early during boot.
>> No migration and no setting of the balloon is involved.
>>
>
> Adding Conny and Halil,
>
> As the QEMU provides no PAGE_HINT feature yet, this quick hack makes the
> guest boot fine again:
>
>
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index 728ecd1eea305..aa2e1864c5736 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -492,7 +492,7 @@ static int init_vqs(struct virtio_balloon *vb)
> callbacks[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL;
> }
>
> - err = vb->vdev->config->find_vqs(vb->vdev, VIRTIO_BALLOON_VQ_MAX,
> + err = vb->vdev->config->find_vqs(vb->vdev, 3, //VIRTIO_BALLOON_VQ_MAX,
> vqs, callbacks, names, NULL, NULL);
> if (err)
> return err;
>
>
> To me it looks like that virtio_ccw_find_vqs will abort if any of the virtqueues
> that it is been asked for does not exist (including the earlier ones).
>

This "hack" makes the random crashes go away, but the balloon interface itself
does not work. (setting the value to anything will hang the guest).
As patch 1 also modifies the main path, there seem to be additional issues, maybe
endianess

Looking at things like

+ vb->cmd_id_received = VIRTIO_BALLOON_CMD_ID_STOP;
+ vb->cmd_id_active = cpu_to_virtio32(vb->vdev,
+ VIRTIO_BALLOON_CMD_ID_STOP);
+ vb->cmd_id_stop = cpu_to_virtio32(vb->vdev,
+ VIRTIO_BALLOON_CMD_ID_STOP);


Why is cmd_id_received not using cpu_to_virtio32?

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