Re: [Qemu-devel] Would virtio support 64 bit address for vring virtqueue?

[Anthony Liguori]

On Wed, Aug 28, 2013 at 4:02 PM, H. Peter Anvin <address@hidden> wrote:
> On 08/28/2013 10:35 AM, Anthony Liguori wrote:
>> Yes, it was originally designed with the 16TB limit in mind.
>>
>> PCI doesn't support 64-bit PIO operations so it would have required a
>> high/low register and additional magic.
>>
>
> s/PCI/x86/

Ack.  Although I wonder if there is a device out there that actually
expects 64-bit writes to a register in an PIO region...

> "Additional magic" is needed only if atomic changes are necessary, but
> in this case this is stuff that is set up during early configuration and
> so isn't an issue.  The "additional magic" needed in that case is latch
> logic - the write to the low part doesn't actually take effect until the
> high part is written.

Well in this case, writing to the PFN is what causes the queue to be
initialized, there isn't a separate status register for this purpose.

Since it's a PIO region, we tried hard to keep the common case within
a 32-byte region and since config space is after the virtio-pci
registers, we tried to keep it as small as possible to maximize
available config space.

Regards,

Anthony Liguori

>
>         -hpa
>