Re: [virtio-comment] [PATCH 1/1] virtio-pmem: Support PCI BAR-relative addresses

[David Hildenbrand <david@redhat.com>]

On 23.07.21 01:26, Taylor Stark wrote:
> On Thu, Jul 22, 2021 at 01:24:17PM +0200, Cornelia Huck wrote:
> > On Wed, Jul 21 2021, tstark@linux.microsoft.com wrote:
> >
> > > From: Taylor Stark <tstark@microsoft.com>
> > >
> > > Update the virtio-pmem RFC spec to add support for describing the pmem region
> > > via PCI BARs. Shared memory windows are used to accomplish this, similar to
> > > virtio-fs and virtio-gpu. This is required to support virtio-pmem in Hyper-V,
> > > since Hyper-V only allows PCI devices to operate on memory ranges defined via
> > > BARs.
> >
> > Given that we already have pmem support out there (even though the spec
> > has not been included yet, should this get a feature?
>
> I wasn't sure if we needed to handle backwards compatibility given that pmem
> hasn't been merged into the spec yet. If we do, then yes I think it makes sense
> to add a feature bit. How about VIRTIO_PMEM_F_SHMEM_REGION?

The implementations that are upstream win, and usually we get a spec 
after the implementation is mature. The spec merely documents what the 
existing implementations are doing. Of course, one can plan ahead and 
propose additions to the spec that won't break existing setups.

The feature seems to be glued to PCI BARs, right? Maybe that should be 
part of the feature name.

--
Thanks,

David / dhildenb