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

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

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


> ---
>  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
> 
>