[PATCH 7/9] hw/display: re-arrange memory region tracking

["Alex Bennée" <alex.bennee@linaro.org>]

QOM objects can be embedded in other QOM objects and managed as part
of their lifetime but this isn't the case for
virtio_gpu_virgl_hostmem_region. However before we can split it out we
need some other way of associating the wider data structure with the
memory region.

Fortunately MemoryRegion has an opaque pointer. This is passed down to
MemoryRegionOps for device type regions but is unused in the
memory_region_init_ram_ptr() case. Use the opaque to carry the
reference and allow the final MemoryRegion object to be reaped when
its reference count is cleared.

Signed-off-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20250410122643.1747913-2-manos.pitsidianakis@linaro.org>
Cc: qemu-stable@nongnu.org
---
 include/system/memory.h       |  1 +
 hw/display/virtio-gpu-virgl.c | 23 ++++++++---------------
 2 files changed, 9 insertions(+), 15 deletions(-)

diff --git a/include/system/memory.h b/include/system/memory.h
index fbbf4cf911..b3cef1acb5 100644
--- a/include/system/memory.h
+++ b/include/system/memory.h
@@ -783,6 +783,7 @@ struct MemoryRegion {
     DeviceState *dev;
 
     const MemoryRegionOps *ops;
+    /* opaque data, used by backends like @ops */
     void *opaque;
     MemoryRegion *container;
     int mapped_via_alias; /* Mapped via an alias, container might be NULL */
diff --git a/hw/display/virtio-gpu-virgl.c b/hw/display/virtio-gpu-virgl.c
index 145a0b3879..71a7500de9 100644
--- a/hw/display/virtio-gpu-virgl.c
+++ b/hw/display/virtio-gpu-virgl.c
@@ -52,17 +52,11 @@ virgl_get_egl_display(G_GNUC_UNUSED void *cookie)
 
 #if VIRGL_VERSION_MAJOR >= 1
 struct virtio_gpu_virgl_hostmem_region {
-    MemoryRegion mr;
+    MemoryRegion *mr;
     struct VirtIOGPU *g;
     bool finish_unmapping;
 };
 
-static struct virtio_gpu_virgl_hostmem_region *
-to_hostmem_region(MemoryRegion *mr)
-{
-    return container_of(mr, struct virtio_gpu_virgl_hostmem_region, mr);
-}
-
 static void virtio_gpu_virgl_resume_cmdq_bh(void *opaque)
 {
     VirtIOGPU *g = opaque;
@@ -73,14 +67,12 @@ static void virtio_gpu_virgl_resume_cmdq_bh(void *opaque)
 static void virtio_gpu_virgl_hostmem_region_free(void *obj)
 {
     MemoryRegion *mr = MEMORY_REGION(obj);
-    struct virtio_gpu_virgl_hostmem_region *vmr;
+    struct virtio_gpu_virgl_hostmem_region *vmr = mr->opaque;
     VirtIOGPUBase *b;
     VirtIOGPUGL *gl;
 
-    vmr = to_hostmem_region(mr);
-    vmr->finish_unmapping = true;
-
     b = VIRTIO_GPU_BASE(vmr->g);
+    vmr->finish_unmapping = true;
     b->renderer_blocked--;
 
     /*
@@ -118,8 +110,8 @@ virtio_gpu_virgl_map_resource_blob(VirtIOGPU *g,
 
     vmr = g_new0(struct virtio_gpu_virgl_hostmem_region, 1);
     vmr->g = g;
+    mr = g_new0(MemoryRegion, 1);
 
-    mr = &vmr->mr;
     memory_region_init_ram_ptr(mr, OBJECT(mr), "blob", size, data);
     memory_region_add_subregion(&b->hostmem, offset, mr);
     memory_region_set_enabled(mr, true);
@@ -131,7 +123,9 @@ virtio_gpu_virgl_map_resource_blob(VirtIOGPU *g,
      * command processing until MR is fully unreferenced and freed.
      */
     OBJECT(mr)->free = virtio_gpu_virgl_hostmem_region_free;
+    mr->opaque = vmr;
 
+    vmr->mr = mr;
     res->mr = mr;
 
     return 0;
@@ -142,16 +136,15 @@ virtio_gpu_virgl_unmap_resource_blob(VirtIOGPU *g,
                                      struct virtio_gpu_virgl_resource *res,
                                      bool *cmd_suspended)
 {
-    struct virtio_gpu_virgl_hostmem_region *vmr;
     VirtIOGPUBase *b = VIRTIO_GPU_BASE(g);
     MemoryRegion *mr = res->mr;
+    struct virtio_gpu_virgl_hostmem_region *vmr;
     int ret;
 
     if (!mr) {
         return 0;
     }
-
-    vmr = to_hostmem_region(res->mr);
+    vmr = mr->opaque;
 
     /*
      * Perform async unmapping in 3 steps:
-- 
2.39.5