[PATCH] virtio_pmem: support feature SHMEM_REGION

[Changyuan Lyu]

As per virtio spec 1.2 section 5.19.5.2, if the feature
VIRTIO_PMEM_F_SHMEM_REGION has been negotiated, the driver MUST query
shared memory ID 0 for the physical address ranges.

Signed-off-by: Changyuan Lyu <changyu...@google.com>
---
 drivers/nvdimm/virtio_pmem.c     | 29 +++++++++++++++++++++++++----
 include/uapi/linux/virtio_pmem.h |  8 ++++++++
 2 files changed, 33 insertions(+), 4 deletions(-)

diff --git a/drivers/nvdimm/virtio_pmem.c b/drivers/nvdimm/virtio_pmem.c
index a92eb172f0e7..5b28d543728b 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 +59,23 @@ 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_SHMCAP_ID);
+               if (!have_shm) {
+                       dev_err(&vdev->dev, "failed to get shared memory region 
%d\n",
+                                       VIRTIO_PMEM_SHMCAP_ID);
+                       return -EINVAL;
+               }
+               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 +137,13 @@ 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..025174f6eacf 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_SHMCAP_ID 0
+
 struct virtio_pmem_config {
        __le64 start;
        __le64 size;
-- 
2.43.0.472.g3155946c3a-goog