virtio_pmem: support feature SHMEM_REGION

This patch adds the support for feature VIRTIO_PMEM_F_SHMEM_REGION
(virtio spec v1.2 section 5.19.5.2 [1]).

During feature negotiation, if VIRTIO_PMEM_F_SHMEM_REGION is offered
by the device, the driver looks for a shared memory region of id 0.
If it is found, this feature is understood. Otherwise, this feature
bit is cleared.

During probe, if VIRTIO_PMEM_F_SHMEM_REGION has been negotiated,
virtio pmem ignores the `start` and `size` fields in device config
and uses 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>
Message-Id: <20231220204906.566922-1-changyuanl@google.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>

Author: Lencerf

drivers/nvdimm/virtio_pmem.c

@@ -29,12 +29,27 @@ static int init_vq(struct virtio_pmem *vpmem)
 	return 0;
 };
 
+static int virtio_pmem_validate(struct virtio_device *vdev)
+{
+	struct virtio_shm_region shm_reg;
+
+	if (virtio_has_feature(vdev, VIRTIO_PMEM_F_SHMEM_REGION) &&
+		!virtio_get_shm_region(vdev, &shm_reg, (u8)VIRTIO_PMEM_SHMEM_REGION_ID)
+	) {
+		dev_notice(&vdev->dev, "failed to get shared memory region %d\n",
+				VIRTIO_PMEM_SHMEM_REGION_ID);
+		__virtio_clear_bit(vdev, VIRTIO_PMEM_F_SHMEM_REGION);
+	}
+	return 0;
+}
+
 static int virtio_pmem_probe(struct virtio_device *vdev)
 {
 	struct nd_region_desc ndr_desc = {};
 	struct nd_region *nd_region;
 	struct virtio_pmem *vpmem;
 	struct resource res;
+	struct virtio_shm_region shm_reg;
 	int err = 0;
 
 	if (!vdev->config->get) {
@@ -57,10 +72,16 @@ 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)) {
+		virtio_get_shm_region(vdev, &shm_reg, (u8)VIRTIO_PMEM_SHMEM_REGION_ID);
+		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;
@@ -122,10 +143,17 @@ 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,
+	.validate		= virtio_pmem_validate,
 	.probe			= virtio_pmem_probe,
 	.remove			= virtio_pmem_remove,
 };

include/uapi/linux/virtio_pmem.h

@@ -14,6 +14,13 @@
 #include <linux/virtio_ids.h>
 #include <linux/virtio_config.h>
 
+/* Feature bits */
+/* guest physical address range will be indicated as shared memory region 0 */
+#define VIRTIO_PMEM_F_SHMEM_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;