[PATCH v3] virtio_pmem: support feature SHMEM_REGION

[Changyuan Lyu <changyuanl@google.com>]

On Tue, Dec 19, 2023 at 11:01 PM Michael S. Tsirkin <mst@redhat.com> wrote:
> 
> This is not a great description. Please describe what the patch does.

Thanks for the feedback! Please see the v3 patch below.

---8<---

This patch adds the support for feature VIRTIO_PMEM_F_SHMEM_REGION
(virtio spec v1.2 section 5.19.5.2 [1]). Feature bit
VIRTIO_PMEM_F_SHMEM_REGION is added to the driver feature
table.

If the driver feature bit VIRTIO_PMEM_F_SHMEM_REGION is found,
during probe, virtio pmem ignores the `start` and `size` fields in
device config and looks for a shared memory region of id 0. The
physical address range of the pmem is then determined by the physical
address range of shared memory region 0.

[1] https://docs.oasis-open.org/virtio/virtio/v1.2/csd01/virtio-v1.2-csd01.html#x1-6480002

Signed-off-by: Changyuan Lyu <changyuanl@google.com>

---
v3:
  * updated the patch description.
V2:
  * renamed VIRTIO_PMEM_SHMCAP_ID to VIRTIO_PMEM_SHMEM_REGION_ID
  * fixed the error handling when region 0 does not exist
---
 drivers/nvdimm/virtio_pmem.c     | 30 ++++++++++++++++++++++++++----
 include/uapi/linux/virtio_pmem.h |  8 ++++++++
 2 files changed, 34 insertions(+), 4 deletions(-)

diff --git a/drivers/nvdimm/virtio_pmem.c b/drivers/nvdimm/virtio_pmem.c
index a92eb172f0e7..8e447c7558cb 100644
--- a/drivers/nvdimm/virtio_pmem.c
+++ b/drivers/nvdimm/virtio_pmem.c
@@ -35,6 +35,8 @@ static int virtio_pmem_probe(struct virtio_device *vdev)
 	struct nd_region *nd_region;
 	struct virtio_pmem *vpmem;
 	struct resource res;
+	struct virtio_shm_region shm_reg;
+	bool have_shm;
 	int err = 0;
 
 	if (!vdev->config->get) {
@@ -57,10 +59,24 @@ 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);
+	if (virtio_has_feature(vdev, VIRTIO_PMEM_F_SHMEM_REGION)) {
+		have_shm = virtio_get_shm_region(vdev, &shm_reg,
+				(u8)VIRTIO_PMEM_SHMEM_REGION_ID);
+		if (!have_shm) {
+			dev_err(&vdev->dev, "failed to get shared memory region %d\n",
+					VIRTIO_PMEM_SHMEM_REGION_ID);
+			err = -ENXIO;
+			goto out_vq;
+		}
+		vpmem->start = shm_reg.addr;
+		vpmem->size = shm_reg.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;
@@ -122,7 +138,13 @@ static void virtio_pmem_remove(struct virtio_device *vdev)
 	virtio_reset_device(vdev);
 }
 
+static unsigned int features[] = {
+	VIRTIO_PMEM_F_SHMEM_REGION,
+};
+
 static struct virtio_driver virtio_pmem_driver = {
+	.feature_table		= features,
+	.feature_table_size	= ARRAY_SIZE(features),
 	.driver.name		= KBUILD_MODNAME,
 	.driver.owner		= THIS_MODULE,
 	.id_table		= id_table,
diff --git a/include/uapi/linux/virtio_pmem.h b/include/uapi/linux/virtio_pmem.h
index d676b3620383..c5e49b6e58b1 100644
--- a/include/uapi/linux/virtio_pmem.h
+++ b/include/uapi/linux/virtio_pmem.h
@@ -14,6 +14,14 @@
 #include <linux/virtio_ids.h>
 #include <linux/virtio_config.h>
 
+/* Feature bits */
+#define VIRTIO_PMEM_F_SHMEM_REGION 0	/* guest physical address range will be
+					 * indicated as shared memory region 0
+					 */
+
+/* shmid of the shared memory region corresponding to the pmem */
+#define VIRTIO_PMEM_SHMEM_REGION_ID 0
+
 struct virtio_pmem_config {
 	__le64 start;
 	__le64 size;
-- 
2.43.0.472.g3155946c3a-goog