linux-kernel - [PATCH] drm/prime: Unbreak virtgpu dma-buf export

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Message-ID: <20240322214801.319975-1-robdclark@gmail.com>
Date: Fri, 22 Mar 2024 14:48:01 -0700
From: Rob Clark <robdclark@...il.com>
To: dri-devel@...ts.freedesktop.org
Cc: Rob Clark <robdclark@...omium.org>,
	Dominik Behr <dbehr@...omium.org>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	David Airlie <airlied@...il.com>,
	Daniel Vetter <daniel@...ll.ch>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	Christian König <christian.koenig@....com>,
	Simon Ser <contact@...rsion.fr>,
	linux-kernel@...r.kernel.org (open list),
	linux-media@...r.kernel.org (open list:DMA BUFFER SHARING FRAMEWORK:Keyword:\bdma_(?:buf|fence|resv)\b),
	linaro-mm-sig@...ts.linaro.org (moderated list:DMA BUFFER SHARING FRAMEWORK:Keyword:\bdma_(?:buf|fence|resv)\b)
Subject: [PATCH] drm/prime: Unbreak virtgpu dma-buf export

From: Rob Clark <robdclark@...omium.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@...omium.org>
Fixes: 207395da5a97 ("drm/prime: reject DMA-BUF attach when get_sg_table is missing")
Signed-off-by: Rob Clark <robdclark@...omium.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