[PATCH] virtio-pmem: Support PCI BAR-relative addresses

[Taylor Stark <tstark@linux.microsoft.com>]

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@linux.microsoft.com>
---
 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
-- 
2.31.1
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