Linux Virtualization - Aug 2020 - [PATCH v3 05/18] virtio: Implement get_shm_region for MMIO transport

From: Sebastien Boeuf <sebastien.boeuf at intel.com>

On MMIO a new set of registers is defined for finding SHM
regions.  Add their definitions and use them to find the region.

Signed-off-by: Sebastien Boeuf <sebastien.boeuf at intel.com>
Cc: kvm at vger.kernel.org
Cc: virtualization at lists.linux-foundation.org
Cc: "Michael S. Tsirkin" <mst at redhat.com>
---
 drivers/virtio/virtio_mmio.c     | 31 +++++++++++++++++++++++++++++++
 include/uapi/linux/virtio_mmio.h | 11 +++++++++++
 2 files changed, 42 insertions(+)

diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c
index 627ac0487494..238383ff1064 100644
--- a/drivers/virtio/virtio_mmio.c
+++ b/drivers/virtio/virtio_mmio.c
@@ -498,6 +498,36 @@ static const char *vm_bus_name(struct virtio_device *vdev)
 	return vm_dev->pdev->name;
 }
 
+static bool vm_get_shm_region(struct virtio_device *vdev,
+			      struct virtio_shm_region *region, u8 id)
+{
+	struct virtio_mmio_device *vm_dev = to_virtio_mmio_device(vdev);
+	u64 len, addr;
+
+	/* Select the region we're interested in */
+	writel(id, vm_dev->base + VIRTIO_MMIO_SHM_SEL);
+
+	/* Read the region size */
+	len = (u64) readl(vm_dev->base + VIRTIO_MMIO_SHM_LEN_LOW);
+	len |= (u64) readl(vm_dev->base + VIRTIO_MMIO_SHM_LEN_HIGH) << 32;
+
+	region->len = len;
+
+	/* Check if region length is -1. If that's the case, the shared memory
+	 * region does not exist and there is no need to proceed further.
+	 */
+	if (len == ~(u64)0)
+		return false;
+
+	/* Read the region base address */
+	addr = (u64) readl(vm_dev->base + VIRTIO_MMIO_SHM_BASE_LOW);
+	addr |= (u64) readl(vm_dev->base + VIRTIO_MMIO_SHM_BASE_HIGH) << 32;
+
+	region->addr = addr;
+
+	return true;
+}
+
 static const struct virtio_config_ops virtio_mmio_config_ops = {
 	.get		= vm_get,
 	.set		= vm_set,
@@ -510,6 +540,7 @@ static const struct virtio_config_ops virtio_mmio_config_ops
= {
 	.get_features	= vm_get_features,
 	.finalize_features = vm_finalize_features,
 	.bus_name	= vm_bus_name,
+	.get_shm_region = vm_get_shm_region,
 };
 
 
diff --git a/include/uapi/linux/virtio_mmio.h b/include/uapi/linux/virtio_mmio.h
index c4b09689ab64..0650f91bea6c 100644
--- a/include/uapi/linux/virtio_mmio.h
+++ b/include/uapi/linux/virtio_mmio.h
@@ -122,6 +122,17 @@
 #define VIRTIO_MMIO_QUEUE_USED_LOW	0x0a0
 #define VIRTIO_MMIO_QUEUE_USED_HIGH	0x0a4
 
+/* Shared memory region id */
+#define VIRTIO_MMIO_SHM_SEL             0x0ac
+
+/* Shared memory region length, 64 bits in two halves */
+#define VIRTIO_MMIO_SHM_LEN_LOW         0x0b0
+#define VIRTIO_MMIO_SHM_LEN_HIGH        0x0b4
+
+/* Shared memory region base address, 64 bits in two halves */
+#define VIRTIO_MMIO_SHM_BASE_LOW        0x0b8
+#define VIRTIO_MMIO_SHM_BASE_HIGH       0x0bc
+
 /* Configuration atomicity value */
 #define VIRTIO_MMIO_CONFIG_GENERATION	0x0fc
 
-- 
2.25.4