Virtualization - Jan 2015 - [PATCH RFC v6 10/20] s390x/virtio-ccw: add virtio set-revision call

On Thu, Dec 11, 2014 at 02:25:12PM +0100, Cornelia Huck
wrote:
> @@ -608,6 +631,25 @@ static int virtio_ccw_cb(SubchDev *sch, CCW1 ccw)
>              }
>          }
>          break;
> +    case CCW_CMD_SET_VIRTIO_REV:
> +        len = sizeof(revinfo);
> +        if (ccw.count < len || (check_len && ccw.count >
len)) {
> +            ret = -EINVAL;
> +            break;
> +        }
> +        if (!ccw.cda) {
> +            ret = -EFAULT;
> +            break;
> +        }
> +        cpu_physical_memory_read(ccw.cda, &revinfo, len);
> +        if (dev->revision >= 0 ||
> +            revinfo.revision > virtio_ccw_rev_max(dev)) {
In the next patch virtio_ccw_handle_set_vq() uses big-endian memory
access functions to load a struct from guest memory.

Here you just copy the struct in without byteswaps.

Are the byteswaps missing here?  (I guess this normally runs big-endian
guests on big-endian hosts so it's not noticable.)

Stefan
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On Tue, 20 Jan 2015 11:08:24 +0000
Stefan Hajnoczi <stefanha at gmail.com> wrote:
> On Thu, Dec 11, 2014 at 02:25:12PM +0100, Cornelia Huck wrote:
> > @@ -608,6 +631,25 @@ static int virtio_ccw_cb(SubchDev *sch, CCW1 ccw)
> >              }
> >          }
> >          break;
> > +    case CCW_CMD_SET_VIRTIO_REV:
> > +        len = sizeof(revinfo);
> > +        if (ccw.count < len || (check_len && ccw.count
> len)) {
> > +            ret = -EINVAL;
> > +            break;
> > +        }
> > +        if (!ccw.cda) {
> > +            ret = -EFAULT;
> > +            break;
> > +        }
> > +        cpu_physical_memory_read(ccw.cda, &revinfo, len);
> > +        if (dev->revision >= 0 ||
> > +            revinfo.revision > virtio_ccw_rev_max(dev)) {
> 
> In the next patch virtio_ccw_handle_set_vq() uses big-endian memory
> access functions to load a struct from guest memory.
> 
> Here you just copy the struct in without byteswaps.
> 
> Are the byteswaps missing here?  (I guess this normally runs big-endian
> guests on big-endian hosts so it's not noticable.)
Indeed, these are supposed to be big-endian. I'll double check the
other payloads.

Thanks for spotting this!

On Wed, 21 Jan 2015 12:23:18 +0100
Cornelia Huck <cornelia.huck at de.ibm.com> wrote:
> On Tue, 20 Jan 2015 11:08:24 +0000
> Stefan Hajnoczi <stefanha at gmail.com> wrote:
> 
> > On Thu, Dec 11, 2014 at 02:25:12PM +0100, Cornelia Huck wrote:
> > > @@ -608,6 +631,25 @@ static int virtio_ccw_cb(SubchDev *sch, CCW1
ccw)
> > >              }
> > >          }
> > >          break;
> > > +    case CCW_CMD_SET_VIRTIO_REV:
> > > +        len = sizeof(revinfo);
> > > +        if (ccw.count < len || (check_len &&
ccw.count > len)) {
> > > +            ret = -EINVAL;
> > > +            break;
> > > +        }
> > > +        if (!ccw.cda) {
> > > +            ret = -EFAULT;
> > > +            break;
> > > +        }
> > > +        cpu_physical_memory_read(ccw.cda, &revinfo, len);
> > > +        if (dev->revision >= 0 ||
> > > +            revinfo.revision > virtio_ccw_rev_max(dev)) {
> > 
> > In the next patch virtio_ccw_handle_set_vq() uses big-endian memory
> > access functions to load a struct from guest memory.
> > 
> > Here you just copy the struct in without byteswaps.
> > 
> > Are the byteswaps missing here?  (I guess this normally runs
big-endian
> > guests on big-endian hosts so it's not noticable.)
> 
> Indeed, these are supposed to be big-endian. I'll double check the
> other payloads.
Right. Cornelia, can you take care of this or shall I rework the patch?

NB: Actually, there are a couple of "XXX config space endianness"
comments in that virtio_ccw_cb() function, so there are likely a bunch
of problems when this code should be run on little endian hosts one day.
So far, this code only runs with big-endian guests on big-endian hosts
since the virtio-ccw machine is currently KVM-only as far as I know,
that's likely why nobody complained about this yet.

 Thomas