If the Guest provides a DMA address that is associated with a ram
device (such as a PCI device region and not its system memory),
then we can obtain the hva (host virtual address) by invoking
address_space_translate() followed by memory_region_get_ram_ptr().

This is because the ram device's address space is not accessible
to virtio-gpu directly and hence dma_memory_map() cannot be used.
Therefore, we first need to identify the memory region associated
with the DMA address and add the offset to the pointer returned
from memory_region_get_ram_ptr() to obtain the host address.

Note that we take a reference on the memory region but we would
still eventually call dma_memory_unmap() (to unref the mr).

Cc: Marc-André Lureau <marcandre.lureau@redhat.com>
Cc: Alex Bennée <alex.bennee@linaro.org>
Cc: Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp>
Cc: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Cc: Alex Williamson <alex@shazbot.org>
Cc: Cédric Le Goater <clg@redhat.com>
Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
---
 hw/display/virtio-gpu.c | 21 ++++++++++++++++++---
 1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/hw/display/virtio-gpu.c b/hw/display/virtio-gpu.c
index 199b18c746..d746c5f426 100644
--- a/hw/display/virtio-gpu.c
+++ b/hw/display/virtio-gpu.c
@@ -798,6 +798,23 @@ static void virtio_gpu_set_scanout_blob(VirtIOGPU *g,
                               &fb, res, &ss.r, &cmd->error);
 }
 
+static void *virtio_gpu_dma_memory_map(VirtIOGPU *g,
+                                       struct virtio_gpu_ctrl_command *cmd,
+                                       uint64_t a, hwaddr *len)
+{
+    MemoryRegion *mr;
+    hwaddr xlat;
+
+    mr = address_space_translate(VIRTIO_DEVICE(g)->dma_as, a, &xlat, len,
+                                 DMA_DIRECTION_TO_DEVICE,
+                                 MEMTXATTRS_UNSPECIFIED);
+    if (memory_region_is_ram(mr)) {
+        memory_region_ref(mr);
+        return memory_region_get_ram_ptr(mr) + xlat;
+    }
+    return NULL;
+}
+
 int virtio_gpu_create_mapping_iov(VirtIOGPU *g,
                                   uint32_t nr_entries, uint32_t offset,
                                   struct virtio_gpu_ctrl_command *cmd,
@@ -839,9 +856,7 @@ int virtio_gpu_create_mapping_iov(VirtIOGPU *g,
 
         do {
             len = l;
-            map = dma_memory_map(VIRTIO_DEVICE(g)->dma_as, a, &len,
-                                 DMA_DIRECTION_TO_DEVICE,
-                                 MEMTXATTRS_UNSPECIFIED);
+            map = virtio_gpu_dma_memory_map(g, cmd, a, &len);
             if (!map) {
                 qemu_log_mask(LOG_GUEST_ERROR, "%s: failed to map MMIO memory for"
                               " element %d\n", __func__, e);
-- 
2.50.1