Re: PCI IO regions must be power of two

[Anthony Liguori <aliguori@us.ibm.com>]

Marcelo Tosatti wrote:
> Anthony,
>
> Both virtio-net and virtio-block currently register PCI IO space regions
> that are not power of two in size.
>
> The decoding process to discover the size of a PCI resource expects it
> to be a power of two. The PCI controller masks the size out of what is
> written into
>
> config_space + 0x10 + (4 * region_num)
>
> The result is that the size is calculated and registered erroneously 
> by the OS:
>
> [root@localhost ~]# cat /proc/ioports  | grep virtio
>   c200-c203 : virtio-pci
>
> This is a virtio-block device whose BAR0 has length (16+20)-1, not 4. 
>
>       BAR0: I/O at 0xc200 [0xc223].
>
> I suggest forcing the size to be power of two as follows:
>
>   

A quick grep of the source show that virtio seems to be the only device 
that isn't behaving here.  I suggest modifying the virtio.c to always 
use a power of two and then perhaps adding a check in hw/pci.c to 
validate that the registered region is a power of two in size.

Regards,

Anthony Liguori

> Index: kvm-userspace.hotplug2/qemu/hw/pci.c
> ===================================================================
> --- kvm-userspace.hotplug2.orig/qemu/hw/pci.c
> +++ kvm-userspace.hotplug2/qemu/hw/pci.c
> @@ -236,6 +236,13 @@ void pci_register_io_region(PCIDevice *p
>
>      if ((unsigned int)region_num >= PCI_NUM_REGIONS)
>          return;
> +
> +    /* IO region size must be power of two */
> +    if (type == PCI_ADDRESS_SPACE_IO && (size & (size-1))) {
> +        size = size << 1;
> +        size &= size-1;
> +    }
> +
>      r = &pci_dev->io_regions[region_num];
>      r->addr = -1;
>      r->size = size;
>
>   


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