On 2025/11/09 14:33, Vivek Kasireddy wrote:
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 figure out if it belongs to a ram device
or not and decide how to obtain the host address accordingly.
Note that we take a reference on the memory region if it belongs
to a ram device but we would still call dma_memory_unmap() later
(to unref mr) regardless of how we obtained the hva.
Cc: Marc-André Lureau <[email protected]>
Cc: Alex Bennée <[email protected]>
Cc: Akihiko Odaki <[email protected]>
Cc: Dmitry Osipenko <[email protected]>
Cc: Alex Williamson <[email protected]>
Cc: Cédric Le Goater <[email protected]>
Signed-off-by: Vivek Kasireddy <[email protected]>
Reviewed-by: Akihiko Odaki <[email protected]>
---
hw/display/virtio-gpu.c | 24 +++++++++++++++++++++---
1 file changed, 21 insertions(+), 3 deletions(-)
diff --git a/hw/display/virtio-gpu.c b/hw/display/virtio-gpu.c
index 199b18c746..d352b5afd6 100644
--- a/hw/display/virtio-gpu.c
+++ b/hw/display/virtio-gpu.c
@@ -798,6 +798,26 @@ 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 = NULL;
+ 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_device(mr)) {
+ memory_region_ref(mr);
+ return memory_region_get_ram_ptr(mr) + xlat;
+ }
+
+ return dma_memory_map(VIRTIO_DEVICE(g)->dma_as, a, len,
+ DMA_DIRECTION_TO_DEVICE,
+ MEMTXATTRS_UNSPECIFIED);
+}
+
int virtio_gpu_create_mapping_iov(VirtIOGPU *g,
uint32_t nr_entries, uint32_t offset,
struct virtio_gpu_ctrl_command *cmd,
@@ -839,9 +859,7 @@ 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);
