Re: large page size virtio issues

[Rusty Russell <rusty@rustcorp.com.au>]

On Wednesday 05 November 2008 09:14:20 Hollis Blanchard wrote:
> Hi Rusty, I'm using a patch that changes the Linux base page size to
> 64K. (This is actually pretty common in ppc64 world, but I happen to be
> trying it on ppc32.)
>
> I'm seeing a problem with virtio. I think at least part of it can be
> explained by qemu's TARGET_PAGE_BITS=12, and the guest's
> PAGE_SHIFT=16. The guest allocates the queue, then passes the pfn (pa
>
> >> PAGE_SHIFT) to the virtio backend (vp_find_vq()). The backend then
>
> calculates the pa as pfn << TARGET_PAGE_BITS.
>
> I have to run right now, but quickly changing qemu TARGET_PAGE_BITS to
> 16 got me a little further but still didn't work. Any thoughts?

I see Anthony hardwired page size into the queue activation ABI for 
virtio_pci.  I think that this should be an actual 4096 (or 12) rather than 
depending on guest page size:

virtio_pci.c:247:
	iowrite32(virt_to_phys(info->queue) >> PAGE_SHIFT,
		  vp_dev->ioaddr + VIRTIO_PCI_QUEUE_PFN);

Anthony?

Cheers,
Rusty.