Hi Akihiko,
> Subject: Re: [PATCH v2 09/10] virtio-gpu-dmabuf: Introduce
> qemu_iovec_same_memory_regions()
>
> On 2025/11/09 14:33, Vivek Kasireddy wrote:
> > Add a helper to check whether the addresses in an iovec array
> > belong to the same memory region or not. This is useful to verify
> > before trying to create a dmabuf from an iovec array.
> >
> > 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]>
> > ---
> > hw/display/virtio-gpu-dmabuf.c | 29 +++++++++++++++++++++++++++++
> > 1 file changed, 29 insertions(+)
> >
> > diff --git a/hw/display/virtio-gpu-dmabuf.c b/hw/display/virtio-gpu-
> dmabuf.c
> > index c34d4c85bc..80143034d4 100644
> > --- a/hw/display/virtio-gpu-dmabuf.c
> > +++ b/hw/display/virtio-gpu-dmabuf.c
> > @@ -27,6 +27,31 @@
> > #include "standard-headers/linux/udmabuf.h"
> > #include "standard-headers/drm/drm_fourcc.h"
> >
> > +static bool qemu_iovec_same_memory_regions(const struct iovec *iov,
> int iov_cnt)
> > +{
> > + RAMBlock *rb, *curr_rb;
> > + ram_addr_t offset;
> > + int i;
> > +
> > + rb = qemu_ram_block_from_host(iov[0].iov_base, false, &offset);
> > + if (!rb) {
> > + qemu_log_mask(LOG_GUEST_ERROR,
> > + "%s: Could not find ramblock/memory region\n",
> > __func__);
> > + return false;
> > + }
> > +
> > + for (i = 1; i < iov_cnt; i++) {
> > + curr_rb = qemu_ram_block_from_host(iov[i].iov_base, false,
> &offset);
> > + if (curr_rb != rb) {
> > + qemu_log_mask(LOG_GUEST_ERROR,
> > + "%s: memory regions not same for iov entries\n",
> > + __func__);
> > + return false;
> > + }
> > + }
> > + return true;
> > +}
> > +
> > static void virtio_gpu_create_udmabuf(struct virtio_gpu_simple_resource
> *res)
> > {
> > struct udmabuf_create_list *list;
> > @@ -137,6 +162,10 @@ void virtio_gpu_init_dmabuf(struct
> virtio_gpu_simple_resource *res)
> > res->iov[0].iov_len < 4096) {
> > pdata = res->iov[0].iov_base;
> > } else {
> > + if (!qemu_iovec_same_memory_regions(res->iov, res->iov_cnt)) {
> > + return;
> > + }
> > +
>
> This check is unnecessary. Perhaps rejecting iov with different memory
> regions may be fine if that simplifies the code, but this actually adds
> some code.
I think we can keep this sanity check but I don't really mind dropping this
patch given that buffers with mixed memory regions are not encountered
in practical situations. Or, I guess I could move the if (curr_rb != rb) check
to virtio_gpu_create_udmabuf() and vfio_device_create_dmabuf_fd()
like you suggested previously.
Thanks,
Vivek
>
> > virtio_gpu_create_udmabuf(res);
> > if (res->dmabuf_fd < 0) {
> > return;
>
> Regards,
> Akihiko Odaki
