This is actually a bit concerning.. importing a host page backed buffer without guest mapping into a passthru device probably doesn't work and should be rejected earlier.

I do think we should relax the restriction (either taking my patch or reverting the commit it fixes) until we work this out properly (because the original patch is a regression), but importing a buffer without guest pages into a passthru device can't possibly work properly. Maybe it works by chance if the host buffer is mapped to the guest, but that is not guaranteed.

BR, -R

On Mon, Mar 25, 2024 at 3:35 PM Dominik Behr dbehr@chromium.org wrote:

It also fixes importing virtgpu blobs into real hardware, for instance amdgpu for DRI_PRIME rendering.

On Fri, Mar 22, 2024 at 2:48 PM Rob Clark robdclark@gmail.com wrote:

...

From: Rob Clark robdclark@chromium.org

virtgpu "vram" GEM objects do not implement obj->get_sg_table(). But they also don't use drm_gem_map_dma_buf(). In fact they may not even have guest visible pages. But it is perfectly fine to export and share with other virtual devices.

Reported-by: Dominik Behr dbehr@chromium.org Fixes: 207395da5a97 ("drm/prime: reject DMA-BUF attach when get_sg_table is missing") Signed-off-by: Rob Clark robdclark@chromium.org

---

drivers/gpu/drm/drm_prime.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c index 7352bde299d5..64dd6276e828 100644 --- a/drivers/gpu/drm/drm_prime.c +++ b/drivers/gpu/drm/drm_prime.c @@ -582,7 +582,12 @@ int drm_gem_map_attach(struct dma_buf *dma_buf, { struct drm_gem_object *obj = dma_buf->priv;

•   if (!obj->funcs->get_sg_table)
  

•   /*
  

•    * drm_gem_map_dma_buf() requires obj->get_sg_table(), but drivers
  

•    * that implement their own ->map_dma_buf() do not.
  

•    */
  

•   if ((dma_buf->ops->map_dma_buf == drm_gem_map_dma_buf) &&
  

•       !obj->funcs->get_sg_table)
            return -ENOSYS;
  
    return drm_gem_pin(obj);
  

-- 2.44.0