Re: [Qemu-devel] [PATCH] virtio: fix descriptor counting in virtqueue_pop

[Stefan Hajnoczi]

On Thu, Oct 05, 2017 at 08:03:35PM +0200, Alexandre DERUMIER wrote:
> Hi,
> 
> has somebody reviewed this patch ?
> 
> I'm also able de reproduce the vm crash like the proxmox user.
> This patch is fixing it for me too.

This patch should go through Michael Tsirkin's tree.  I have pinged him
separately in case this email thread got buried in his inbox.

Stefan

> 
> Regards,
> 
> Alexandre
> 
> 
> ----- Mail original -----
> De: "Wolfgang Bumiller" <address@hidden>
> À: "qemu-devel" <address@hidden>
> Cc: "pbonzini" <address@hidden>, "Michael S. Tsirkin" <address@hidden>
> Envoyé: Mercredi 20 Septembre 2017 08:09:33
> Objet: [Qemu-devel] [PATCH] virtio: fix descriptor counting in virtqueue_pop
> 
> While changing the s/g list allocation, commit 3b3b0628 
> also changed the descriptor counting to count iovec entries 
> as split by cpu_physical_memory_map(). Previously only the 
> actual descriptor entries were counted and the split into 
> the iovec happened afterwards in virtqueue_map(). 
> Count the entries again instead to avoid erroneous 
> "Looped descriptor" errors. 
> 
> Reported-by: Hans Middelhoek <address@hidden> 
> Link: https://forum.proxmox.com/threads/vm-crash-with-memory-hotplug.35904/ 
> Fixes: 3b3b0628217e ("virtio: slim down allocation of VirtQueueElements") 
> Signed-off-by: Wolfgang Bumiller <address@hidden> 
> --- 
> hw/virtio/virtio.c | 6 +++--- 
> 1 file changed, 3 insertions(+), 3 deletions(-) 
> 
> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c 
> index 890b4d7eb7..33bb770177 100644 
> --- a/hw/virtio/virtio.c 
> +++ b/hw/virtio/virtio.c 
> @@ -834,7 +834,7 @@ void *virtqueue_pop(VirtQueue *vq, size_t sz) 
> int64_t len; 
> VirtIODevice *vdev = vq->vdev; 
> VirtQueueElement *elem = NULL; 
> - unsigned out_num, in_num; 
> + unsigned out_num, in_num, elem_entries; 
> hwaddr addr[VIRTQUEUE_MAX_SIZE]; 
> struct iovec iov[VIRTQUEUE_MAX_SIZE]; 
> VRingDesc desc; 
> @@ -852,7 +852,7 @@ void *virtqueue_pop(VirtQueue *vq, size_t sz) 
> smp_rmb(); 
> 
> /* When we start there are none of either input nor output. */ 
> - out_num = in_num = 0; 
> + out_num = in_num = elem_entries = 0; 
> 
> max = vq->vring.num; 
> 
> @@ -922,7 +922,7 @@ void *virtqueue_pop(VirtQueue *vq, size_t sz) 
> } 
> 
> /* If we've got too many, that implies a descriptor loop. */ 
> - if ((in_num + out_num) > max) { 
> + if (++elem_entries > max) { 
> virtio_error(vdev, "Looped descriptor"); 
> goto err_undo_map; 
> } 
> -- 
> 2.11.0 
> 
>

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