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SubjectRe: vhost changes (batched) in linux-next after 12/13 trigger random crashes in KVM guests after reboot
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On Tue, 2020-02-11 at 14:13 +0100, Christian Borntraeger wrote:
>
> On 11.02.20 14:04, Eugenio Pérez wrote:
> > On Mon, 2020-02-10 at 12:01 +0100, Christian Borntraeger wrote:
> > > On 10.02.20 10:47, Eugenio Perez Martin wrote:
> > > > Hi Christian.
> > > >
> > > > I'm not able to reproduce the failure with eccb852f1fe6bede630e2e4f1a121a81e34354ab commit. Could you add more
> > > > data?
> > > > Your configuration (libvirt or qemu line), and host's dmesg output if any?
> > > >
> > > > Thanks!
> > >
> > > If it was not obvious, this is on s390x, a big endian system.
> > >
> >
> > Hi Christian. Thank you very much for your fast responses.
> >
> > Could you try this patch on top of eccb852f1fe6bede630e2e4f1a121a81e34354ab?
>
> I still get
> [ 43.665145] Guest moved used index from 0 to 289
> after some reboots.
>
>
> > Thanks!
> >
> > From 71d0f9108a18aa894cc0c0c1c7efbad39f465a27 Mon Sep 17 00:00:00 2001
> > From: =?UTF-8?q?Eugenio=20P=C3=A9rez?= <
> > eperezma@redhat.com>
> > Date: Tue, 11 Feb 2020 13:19:10 +0100
> > Subject: [PATCH] vhost: fix return value of vhost_get_vq_desc
> >
> > Before of the batch change, it was the chain's head. Need to keep that
> > way or we will not be able to free a chain of descriptors.
> >
> > Fixes: eccb852f1fe6 ("vhost: batching fetches")
> > ---
> > drivers/vhost/vhost.c | 3 +--
> > 1 file changed, 1 insertion(+), 2 deletions(-)
> >
> > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> > index b5a51b1f2e79..fc422c3e5c08 100644
> > --- a/drivers/vhost/vhost.c
> > +++ b/drivers/vhost/vhost.c
> > @@ -2409,12 +2409,11 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
> > *out_num += ret;
> > }
> >
> > - ret = desc->id;
> > -
> > if (!(desc->flags & VRING_DESC_F_NEXT))
> > break;
> > }
> >
> > + ret = vq->descs[vq->first_desc].id;
> > vq->first_desc = i + 1;
> >
> > return ret;
> >

Sorry, still not able to reproduce the issue.

Could we try to disable all the vhost features?

Thanks!

diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 661088ae6dc7..08f6d2ccb697 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -250,11 +250,11 @@ int vhost_init_device_iotlb(struct vhost_dev *d, bool enabled);
} while (0)

enum {
- VHOST_FEATURES = (1ULL << VIRTIO_F_NOTIFY_ON_EMPTY) |
- (1ULL << VIRTIO_RING_F_INDIRECT_DESC) |
- (1ULL << VIRTIO_RING_F_EVENT_IDX) |
- (1ULL << VHOST_F_LOG_ALL) |
- (1ULL << VIRTIO_F_ANY_LAYOUT) |
+ VHOST_FEATURES = /* (1ULL << VIRTIO_F_NOTIFY_ON_EMPTY) | */
+ /* (1ULL << VIRTIO_RING_F_INDIRECT_DESC) | */
+ /* (1ULL << VIRTIO_RING_F_EVENT_IDX) | */
+ /* (1ULL << VHOST_F_LOG_ALL) | */
+ /* (1ULL << VIRTIO_F_ANY_LAYOUT) | */
(1ULL << VIRTIO_F_VERSION_1)
};
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