"Kim, Dongwon" <[email protected]> writes:
> Hi Marc-André,
>
>> -----Original Message-----
>> From: Marc-André Lureau <[email protected]>
>> Sent: Tuesday, March 3, 2026 8:28 AM
>> To: Kim, Dongwon <[email protected]>
>> Cc: [email protected]
>> Subject: Re: [PATCH] virtio-gpu: Fix scanout dmabuf cleanup during resource
>> destruction
>>
>> Hi
>>
>> On Tue, Mar 3, 2026 at 2:06 AM <[email protected]> wrote:
>> >
>> > From: Dongwon Kim <[email protected]>
>> >
>> > When a virtio-gpu resource is destroyed, any associated udmabuf must
>> > be properly torn down. Currently, the code may leave dangling
>> > references to dmabuf file descriptors in the scanout primary buffers.
>> >
>> > This patch updates virtio_gpu_fini_udmabuf to:
>> > 1. Iterate through all active scanouts.
>> > 2. Identify dmabufs that match the resource's file descriptor.
>> > 3. Close the dmabuf and invalidate the resource's FD reference to
>> > prevent use-after-free or double-close scenarios.
>> > 4. Finally, trigger the underlying udmabuf destruction.
>> >
>> > This ensures that the display backend does not attempt to access
>> > memory or FDs that have been released by the guest or the host.
>> >
>> > Cc: Gerd Hoffmann <[email protected]>
>> > Cc: Marc-André Lureau <[email protected]>
>> > Signed-off-by: Vivek Kasireddy <[email protected]>
>> > Signed-off-by: Dongwon Kim <[email protected]>
>>
>> Acked-by: Marc-André Lureau <[email protected]>
>>
>> > ---
>> > include/hw/virtio/virtio-gpu.h | 3 ++-
>> > hw/display/virtio-gpu-udmabuf.c | 25 ++++++++++++++++++-------
>> > hw/display/virtio-gpu.c | 2 +-
>> > 3 files changed, 21 insertions(+), 9 deletions(-)
>> >
>> > diff --git a/include/hw/virtio/virtio-gpu.h
>> > b/include/hw/virtio/virtio-gpu.h index 58e0f91fda..65312f869d 100644
>> > --- a/include/hw/virtio/virtio-gpu.h
>> > +++ b/include/hw/virtio/virtio-gpu.h
>> > @@ -357,7 +357,8 @@ bool virtio_gpu_scanout_blob_to_fb(struct
>> > virtio_gpu_framebuffer *fb,
>> > /* virtio-gpu-udmabuf.c */
>> > bool virtio_gpu_have_udmabuf(void);
>> > void virtio_gpu_init_udmabuf(struct virtio_gpu_simple_resource *res);
>> > -void virtio_gpu_fini_udmabuf(struct virtio_gpu_simple_resource *res);
>> > +void virtio_gpu_fini_udmabuf(VirtIOGPU *g,
>> > + struct virtio_gpu_simple_resource *res);
>> > int virtio_gpu_update_dmabuf(VirtIOGPU *g,
>> > uint32_t scanout_id,
>> > struct virtio_gpu_simple_resource *res,
>> > diff --git a/hw/display/virtio-gpu-udmabuf.c
>> > b/hw/display/virtio-gpu-udmabuf.c index d804f321aa..bd5b44f5fb 100644
>> > --- a/hw/display/virtio-gpu-udmabuf.c
>> > +++ b/hw/display/virtio-gpu-udmabuf.c
>> > @@ -151,13 +151,6 @@ void virtio_gpu_init_udmabuf(struct
>> virtio_gpu_simple_resource *res)
>> > res->blob = pdata;
>> > }
>> >
>> > -void virtio_gpu_fini_udmabuf(struct virtio_gpu_simple_resource *res)
>> > -{
>> > - if (res->remapped) {
>> > - virtio_gpu_destroy_udmabuf(res);
>> > - }
>> > -}
>> > -
>> > static void virtio_gpu_free_dmabuf(VirtIOGPU *g, VGPUDMABuf *dmabuf)
>> > {
>> > struct virtio_gpu_scanout *scanout; @@ -169,6 +162,24 @@ static
>> > void virtio_gpu_free_dmabuf(VirtIOGPU *g, VGPUDMABuf *dmabuf)
>> > g_free(dmabuf);
>> > }
>> >
>> > +void virtio_gpu_fini_udmabuf(VirtIOGPU *g, struct
>> > +virtio_gpu_simple_resource *res) {
>> > + int max_outputs = g->parent_obj.conf.max_outputs;
>> > + int i;
>> > +
>> > + for (i = 0; i < max_outputs; i++) {
>> > + VGPUDMABuf *dmabuf = g->dmabuf.primary[i];
>> > +
>> > + if (dmabuf && (res->dmabuf_fd != -1) &&
>>
>> Maybe add qemu_dmabuf_get_numplanes() > 0 ?
>
> Do you want me to add this condition and resubmit v2 of this patch? I saw
> this patch has already been in the queue.
If you send v2 I can swap it out.
>
>>
>> > + qemu_dmabuf_get_fds(dmabuf->buf, NULL)[0] == res->dmabuf_fd) {
>> > + qemu_dmabuf_close(dmabuf->buf);
>> > + res->dmabuf_fd = -1;
>>
>> I am not really happy about that we close the underlying fd here before the
>> next destroy, but I don't have an immediate solution
>
> Yeah, I just thought this would be the best for now.
>
>>
>> > + }
>> > + }
>> > +
>> > + virtio_gpu_destroy_udmabuf(res);
>> > +}
>> > +
>> > static VGPUDMABuf
>> > *virtio_gpu_create_dmabuf(VirtIOGPU *g,
>> > uint32_t scanout_id, diff --git
>> > a/hw/display/virtio-gpu.c b/hw/display/virtio-gpu.c index
>> > 643e91ca2a..b2af861f0d 100644
>> > --- a/hw/display/virtio-gpu.c
>> > +++ b/hw/display/virtio-gpu.c
>> > @@ -902,7 +902,7 @@ void virtio_gpu_cleanup_mapping(VirtIOGPU *g,
>> > res->addrs = NULL;
>> >
>> > if (res->blob) {
>> > - virtio_gpu_fini_udmabuf(res);
>> > + virtio_gpu_fini_udmabuf(g, res);
>> > }
>> > }
>> >
>> > --
>> > 2.43.0
>> >
>> >
>>
>>
>> --
>> Marc-André Lureau
>
> Thanks,
--
Alex Bennée
Virtualisation Tech Lead @ Linaro
