From: Thomas Zimmermann <tzimmermann@suse.de>
To: airlied@redhat.com, daniel@ffwll.ch,
maarten.lankhorst@linux.intel.com, mripard@kernel.org,
hdegoede@redhat.com, christian.koenig@amd.com
Cc: Thomas Zimmermann <tzimmermann@suse.de>, dri-devel@lists.freedesktop.org
Subject: [PATCH 1/8] drm/gem: Write down some rules for vmap usage
Date: Mon, 30 Nov 2020 13:04:26 +0100 [thread overview]
Message-ID: <20201130120433.7205-2-tzimmermann@suse.de> (raw)
In-Reply-To: <20201130120433.7205-1-tzimmermann@suse.de>
Mapping a GEM object's buffer into kernel address space prevents the
buffer from being evicted from VRAM, which in turn may result in
out-of-memory errors. It's therefore required to only vmap GEM BOs for
short periods of time; unless the GEM implementation provides additional
guarantees.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
---
drivers/gpu/drm/drm_prime.c | 6 ++++++
include/drm/drm_gem.h | 16 ++++++++++++++++
2 files changed, 22 insertions(+)
diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index 7db55fce35d8..9c9ece9833e0 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -669,6 +669,12 @@ EXPORT_SYMBOL(drm_gem_unmap_dma_buf);
* callback. Calls into &drm_gem_object_funcs.vmap for device specific handling.
* The kernel virtual address is returned in map.
*
+ * To prevent the GEM object from being relocated, callers must hold the GEM
+ * object's reservation lock from when calling this function until releasing the
+ * mapping. Holding onto a mapping and the associated reservation lock for an
+ * unbound time may result in out-of-memory errors. Calls to drm_gem_dmabuf_vmap()
+ * should therefore be accompanied by a call to drm_gem_dmabuf_vunmap().
+ *
* Returns 0 on success or a negative errno code otherwise.
*/
int drm_gem_dmabuf_vmap(struct dma_buf *dma_buf, struct dma_buf_map *map)
diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h
index 5e6daa1c982f..7c34cd5ec261 100644
--- a/include/drm/drm_gem.h
+++ b/include/drm/drm_gem.h
@@ -137,7 +137,21 @@ struct drm_gem_object_funcs {
* Returns a virtual address for the buffer. Used by the
* drm_gem_dmabuf_vmap() helper.
*
+ * Notes to implementors:
+ *
+ * - Implementations must expect pairs of @vmap and @vunmap to be
+ * called frequently and should optimize for this case.
+ *
+ * - Implemenations may expect the caller to hold the GEM object's
+ * reservation lock to protect against concurrent calls and relocation
+ * of the GEM object.
+ *
+ * - Implementations may provide additional guarantees (e.g., working
+ * without holding the reservation lock).
+ *
* This callback is optional.
+ *
+ * See also drm_gem_dmabuf_vmap()
*/
int (*vmap)(struct drm_gem_object *obj, struct dma_buf_map *map);
@@ -148,6 +162,8 @@ struct drm_gem_object_funcs {
* drm_gem_dmabuf_vunmap() helper.
*
* This callback is optional.
+ *
+ * See also @vmap.
*/
void (*vunmap)(struct drm_gem_object *obj, struct dma_buf_map *map);
--
2.29.2
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next prev parent reply other threads:[~2020-11-30 12:04 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-30 12:04 [PATCH 0/8] drm/vram-helper: Lock GEM BOs while they are mapped Thomas Zimmermann
2020-11-30 12:04 ` Thomas Zimmermann [this message]
2020-11-30 15:30 ` [PATCH 1/8] drm/gem: Write down some rules for vmap usage Daniel Vetter
2020-11-30 15:33 ` Christian König
2020-12-01 8:32 ` Thomas Zimmermann
2020-12-01 9:10 ` Daniel Vetter
2020-12-01 9:40 ` Thomas Zimmermann
2020-12-01 10:00 ` Daniel Vetter
2020-12-01 10:27 ` Thomas Zimmermann
2020-12-01 10:34 ` Christian König
2020-12-01 11:30 ` Thomas Zimmermann
2020-12-01 12:14 ` Christian König
2020-12-01 12:33 ` Thomas Zimmermann
2020-12-01 12:38 ` Christian König
2020-12-01 12:51 ` Thomas Zimmermann
2020-12-01 12:53 ` Thomas Zimmermann
2020-12-01 13:05 ` Christian König
2020-12-01 16:54 ` Daniel Vetter
2020-12-01 12:05 ` Thomas Zimmermann
2020-12-01 9:13 ` Christian König
2020-12-01 9:30 ` Thomas Zimmermann
2020-12-01 8:15 ` Thomas Zimmermann
2020-11-30 12:04 ` [PATCH 2/8] drm/ast: Only map cursor BOs during updates Thomas Zimmermann
2020-11-30 12:04 ` [PATCH 3/8] drm/vram-helper: Provide drm_gem_vram_vmap_unlocked() Thomas Zimmermann
2020-11-30 12:04 ` [PATCH 4/8] drm/ast: Use drm_gem_vram_vmap_unlocked() in ast_cursor_show() Thomas Zimmermann
2020-11-30 12:04 ` [PATCH 5/8] drm/vboxvideo: Use drm_gem_vram_vmap_unlocked() in cursor update Thomas Zimmermann
2020-11-30 12:04 ` [PATCH 6/8] drm/vram-helper: Remove pinning and locking from drm_gem_vram_vmap() Thomas Zimmermann
2020-11-30 12:04 ` [PATCH 7/8] drm/vram-helper: Remove vmap reference counting Thomas Zimmermann
2020-11-30 12:04 ` [PATCH 8/8] drm/vram-helper: Simplify vmap implementation Thomas Zimmermann
2020-11-30 12:27 ` [PATCH 0/8] drm/vram-helper: Lock GEM BOs while they are mapped Christian König
2020-11-30 12:45 ` Thomas Zimmermann
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