Re: [PATCH v4 09/17] hw/display: re-arrange memory region tracking

[Akihiko Odaki <akihiko.odaki@daynix.com>]

On 2025/06/03 20:01, Alex Bennée wrote:
> 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 fc35a0dcad..90715ff44a 100644
> --- a/include/system/memory.h
> +++ b/include/system/memory.h
> @@ -784,6 +784,7 @@ 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);

This patch does nothing more than adding a separate allocation for 
MemoryRegion. Besides there is no corresponding g_free(). This patch can 
be simply dropped.

Regards,
Akihiko Odaki

>   
> -    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: