On Mon, Dec 12, 2011 at 09:15:03AM +1030, Rusty Russell wrote:
> On Sun, 11 Dec 2011 11:42:56 +0200, "Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote:
> > On Thu, Dec 08, 2011 at 09:09:33PM +1030, Rusty Russell wrote:
> > > +/* There is no iowrite64. We use two 32-bit ops. */
> > > +static void iowrite64(u64 val, const __le64 *addr)
> > > +{
> > > + iowrite32((u32)val, (__le32 *)addr);
> > > + iowrite32(val >> 32, (__le32 *)addr + 1);
> > > +}
> > > +
> >
> > Let's put addr_lo/addr_hi in the structure then,
> > to make the fact this field is not atomic explicit?
>
> Good point, assuming I haven't missed something.
>
> Are 64-bit accesses actually unknown in PCI-land? Or is this a limited
> availability thing?
>
> Thanks,
> Rusty.
By the way, a generic question on virtio-pci: we now have:
/* virtio config->get() implementation */
static void vp_get(struct virtio_device *vdev, unsigned offset,
void *buf, unsigned len)
{
struct virtio_pci_device *vp_dev = to_vp_device(vdev);
void __iomem *ioaddr = vp_dev->ioaddr +
VIRTIO_PCI_CONFIG(vp_dev) + offset;
u8 *ptr = buf;
int i;
for (i = 0; i < len; i++)
ptr[i] = ioread8(ioaddr + i);
}
This means that if configuration is read while
it is changed, we might get an inconsistent state,
with parts of a 64 bit field coming from old
and parts from new value.
Isn't this a problem?
--
MST
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