Re: [PATCH v2 1/2] virtio-pmem: Support PCI BAR-relative addresses

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Jul 19, 2021 at 11:41:03PM -0700, Taylor Stark wrote:
> On Mon, Jul 19, 2021 at 05:17:00PM -0400, Michael S. Tsirkin wrote:
> > On Thu, Jul 15, 2021 at 03:35:05PM -0700, Taylor Stark wrote:
> > > Update virtio-pmem to allow for the pmem region to be specified in either
> > > guest absolute terms or as a PCI BAR-relative address. This is required
> > > to support virtio-pmem in Hyper-V, since Hyper-V only allows PCI devices
> > > to operate on PCI memory ranges defined via BARs.
> > > 
> > > Virtio-pmem will check for a shared memory window and use that if found,
> > > else it will fallback to using the guest absolute addresses in
> > > virtio_pmem_config. This was chosen over defining a new feature bit,
> > > since it's similar to how virtio-fs is configured.
> > > 
> > > Signed-off-by: Taylor Stark <tstark@microsoft.com>
> > 
> > This needs to be added to the device spec too.
> > Can you send a spec patch please?
> > It's a subscriber-only list virtio-comment@lists.oasis-open.org
> 
> Absolutely! I tried looking on the virtio-spec repo on github but
> I couldn't find a spec for virtio-pmem to update. There is this
> issue (https://github.com/oasis-tcs/virtio-spec/issues/78) which
> seems to indicate the virtio-pmem spec hasn't been added yet.
> Any suggestions for where to send a patch?
> 
> Thanks,
> Taylor 

Just apply that patch (whichever you think is right)
and do yours on top and indicate this in the email.
Send it to virtio-comments.

> > > ---
> > >  drivers/nvdimm/virtio_pmem.c | 21 +++++++++++++++++----
> > >  drivers/nvdimm/virtio_pmem.h |  3 +++
> > >  2 files changed, 20 insertions(+), 4 deletions(-)
> > > 
> > > diff --git a/drivers/nvdimm/virtio_pmem.c b/drivers/nvdimm/virtio_pmem.c
> > > index 726c7354d465..43c1d835a449 100644
> > > --- a/drivers/nvdimm/virtio_pmem.c
> > > +++ b/drivers/nvdimm/virtio_pmem.c
> > > @@ -37,6 +37,8 @@ static int virtio_pmem_probe(struct virtio_device *vdev)
> > >  	struct virtio_pmem *vpmem;
> > >  	struct resource res;
> > >  	int err = 0;
> > > +	bool have_shm_region;
> > > +	struct virtio_shm_region pmem_region;
> > >  
> > >  	if (!vdev->config->get) {
> > >  		dev_err(&vdev->dev, "%s failure: config access disabled\n",
> > > @@ -58,10 +60,21 @@ static int virtio_pmem_probe(struct virtio_device *vdev)
> > >  		goto out_err;
> > >  	}
> > >  
> > > -	virtio_cread_le(vpmem->vdev, struct virtio_pmem_config,
> > > -			start, &vpmem->start);
> > > -	virtio_cread_le(vpmem->vdev, struct virtio_pmem_config,
> > > -			size, &vpmem->size);
> > > +	/* Retrieve the pmem device's address and size. It may have been supplied
> > > +	 * as a PCI BAR-relative shared memory region, or as a guest absolute address.
> > > +	 */
> > > +	have_shm_region = virtio_get_shm_region(vpmem->vdev, &pmem_region,
> > > +						VIRTIO_PMEM_SHMCAP_ID_PMEM_REGION);
> > > +
> > > +	if (have_shm_region) {
> > > +		vpmem->start = pmem_region.addr;
> > > +		vpmem->size = pmem_region.len;
> > > +	} else {
> > > +		virtio_cread_le(vpmem->vdev, struct virtio_pmem_config,
> > > +				start, &vpmem->start);
> > > +		virtio_cread_le(vpmem->vdev, struct virtio_pmem_config,
> > > +				size, &vpmem->size);
> > > +	}
> > >  
> > >  	res.start = vpmem->start;
> > >  	res.end   = vpmem->start + vpmem->size - 1;
> > > diff --git a/drivers/nvdimm/virtio_pmem.h b/drivers/nvdimm/virtio_pmem.h
> > > index 0dddefe594c4..62bb564e81cb 100644
> > > --- a/drivers/nvdimm/virtio_pmem.h
> > > +++ b/drivers/nvdimm/virtio_pmem.h
> > > @@ -50,6 +50,9 @@ struct virtio_pmem {
> > >  	__u64 size;
> > >  };
> > >  
> > > +/* For the id field in virtio_pci_shm_cap */
> > > +#define VIRTIO_PMEM_SHMCAP_ID_PMEM_REGION 0
> > > +
> > >  void virtio_pmem_host_ack(struct virtqueue *vq);
> > >  int async_pmem_flush(struct nd_region *nd_region, struct bio *bio);
> > >  #endif
> > > -- 
> > > 2.32.0