[Intel-gfx] [PATCH v3 4/5] drm/i915/gem: Fix same-driver-another-instance dma-buf export

Mon Jun 28 19:45:31 UTC 2021

>-----Original Message-----
>From: Thomas Hellström <thomas.hellstrom at linux.intel.com>
>Sent: Monday, June 28, 2021 10:46 AM
>To: intel-gfx at lists.freedesktop.org; dri-devel at lists.freedesktop.org
>Cc: Auld, Matthew <matthew.auld at intel.com>;
>maarten.lankhorst at linux.intel.com; Thomas Hellström
><thomas.hellstrom at linux.intel.com>; Ruhl; Ruhl, Michael J
><michael.j.ruhl at intel.com>
>Subject: [PATCH v3 4/5] drm/i915/gem: Fix same-driver-another-instance
>dma-buf export
>
>If our exported dma-bufs are imported by another instance of our driver,
>that instance will typically have the imported dma-bufs locked during
>map_attachment(). But the exporter also locks the same reservation
>object in the map_dma_buf() callback, which leads to recursive locking.
>
>Add a live selftest to catch this case, and as a workaround until
>we fully support dynamic import and export, declare the exporter dynamic
>by providing NOP pin() and unpin() functions. This means our map_dma_buf()
>callback will *always* get called locked, and by pinning unconditionally
>in i915_gem_map_dma_buf() we make sure we don't need to use the
>move_notify() functionality which is not yet implemented.

An interesting abuse of the interface, but it seems reasonable (for now) to me.

Reviewed-by: Michael J. Ruhl <michael.j.ruhl at intel.com>

Mike

>Reported-by: Ruhl, Michael J <michael.j.ruhl at intel.com>
>Cc: Ruhl, Michael J <michael.j.ruhl at intel.com>
>Signed-off-by: Thomas Hellström <thomas.hellstrom at linux.intel.com>
>---
> drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c    | 31 ++++++-
> .../drm/i915/gem/selftests/i915_gem_dmabuf.c  | 81
>++++++++++++++++++-
> 2 files changed, 108 insertions(+), 4 deletions(-)
>
>diff --git a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
>b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
>index 616c3a2f1baf..1d1eeb167d28 100644
>--- a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
>+++ b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
>@@ -12,6 +12,8 @@
> #include "i915_gem_object.h"
> #include "i915_scatterlist.h"
>
>+I915_SELFTEST_DECLARE(static bool force_different_devices;)
>+
> static struct drm_i915_gem_object *dma_buf_to_obj(struct dma_buf *buf)
> {
> 	return to_intel_bo(buf->priv);
>@@ -25,7 +27,9 @@ static struct sg_table *i915_gem_map_dma_buf(struct
>dma_buf_attachment *attachme
> 	struct scatterlist *src, *dst;
> 	int ret, i;
>
>-	ret = i915_gem_object_pin_pages_unlocked(obj);
>+	assert_object_held(obj);
>+
>+	ret = i915_gem_object_pin_pages(obj);
> 	if (ret)
> 		goto err;
>
>@@ -168,6 +172,26 @@ static int i915_gem_end_cpu_access(struct dma_buf
>*dma_buf, enum dma_data_direct
> 	return err;
> }
>
>+/*
>+ * As a workaround until we fully support dynamic import and export,
>+ * declare the exporter dynamic by providing NOP pin() and unpin()
>functions.
>+ * This means our i915_gem_map_dma_buf() callback will *always* get
>called
>+ * locked, and by pinning unconditionally in i915_gem_map_dma_buf() we
>make
>+ * sure we don't need to use the move_notify() functionality which is
>+ * not yet implemented. Typically for the same-driver-another-instance case,
>+ * i915_gem_map_dma_buf() will be called at importer attach time and the
>+ * mapped sg_list will be cached by the dma-buf core for the
>+ * duration of the attachment.
>+ */
>+static int i915_gem_dmabuf_pin(struct dma_buf_attachment *attach)
>+{
>+	return 0;
>+}
>+
>+static void i915_gem_dmabuf_unpin(struct dma_buf_attachment *attach)
>+{
>+}
>+
> static const struct dma_buf_ops i915_dmabuf_ops =  {
> 	.map_dma_buf = i915_gem_map_dma_buf,
> 	.unmap_dma_buf = i915_gem_unmap_dma_buf,
>@@ -177,6 +201,8 @@ static const struct dma_buf_ops i915_dmabuf_ops =  {
> 	.vunmap = i915_gem_dmabuf_vunmap,
> 	.begin_cpu_access = i915_gem_begin_cpu_access,
> 	.end_cpu_access = i915_gem_end_cpu_access,
>+	.pin = i915_gem_dmabuf_pin,
>+	.unpin = i915_gem_dmabuf_unpin,
> };
>
> struct dma_buf *i915_gem_prime_export(struct drm_gem_object
>*gem_obj, int flags)
>@@ -241,7 +267,8 @@ struct drm_gem_object
>*i915_gem_prime_import(struct drm_device *dev,
> 	if (dma_buf->ops == &i915_dmabuf_ops) {
> 		obj = dma_buf_to_obj(dma_buf);
> 		/* is it from our device? */
>-		if (obj->base.dev == dev) {
>+		if (obj->base.dev == dev &&
>+		    !I915_SELFTEST_ONLY(force_different_devices)) {
> 			/*
> 			 * Importing dmabuf exported from out own gem
>increases
> 			 * refcount on gem itself instead of f_count of
>dmabuf.
>diff --git a/drivers/gpu/drm/i915/gem/selftests/i915_gem_dmabuf.c
>b/drivers/gpu/drm/i915/gem/selftests/i915_gem_dmabuf.c
>index dd74bc09ec88..24735d6c12a2 100644
>--- a/drivers/gpu/drm/i915/gem/selftests/i915_gem_dmabuf.c
>+++ b/drivers/gpu/drm/i915/gem/selftests/i915_gem_dmabuf.c
>@@ -35,7 +35,7 @@ static int igt_dmabuf_export(void *arg)
> static int igt_dmabuf_import_self(void *arg)
> {
> 	struct drm_i915_private *i915 = arg;
>-	struct drm_i915_gem_object *obj;
>+	struct drm_i915_gem_object *obj, *import_obj;
> 	struct drm_gem_object *import;
> 	struct dma_buf *dmabuf;
> 	int err;
>@@ -65,14 +65,90 @@ static int igt_dmabuf_import_self(void *arg)
> 		err = -EINVAL;
> 		goto out_import;
> 	}
>+	import_obj = to_intel_bo(import);
>+
>+	i915_gem_object_lock(import_obj, NULL);
>+	err = ____i915_gem_object_get_pages(import_obj);
>+	i915_gem_object_unlock(import_obj);
>+	if (err) {
>+		pr_err("Same object dma-buf get_pages failed!\n");
>+		goto out_import;
>+	}
>
> 	err = 0;
> out_import:
>-	i915_gem_object_put(to_intel_bo(import));
>+	i915_gem_object_put(import_obj);
>+out_dmabuf:
>+	dma_buf_put(dmabuf);
>+out:
>+	i915_gem_object_put(obj);
>+	return err;
>+}
>+
>+static int igt_dmabuf_import_same_driver(void *arg)
>+{
>+	struct drm_i915_private *i915 = arg;
>+	struct drm_i915_gem_object *obj, *import_obj;
>+	struct drm_gem_object *import;
>+	struct dma_buf *dmabuf;
>+	int err;
>+
>+	force_different_devices = true;
>+	obj = i915_gem_object_create_shmem(i915, PAGE_SIZE);
>+	if (IS_ERR(obj))
>+		goto out_ret;
>+
>+	dmabuf = i915_gem_prime_export(&obj->base, 0);
>+	if (IS_ERR(dmabuf)) {
>+		pr_err("i915_gem_prime_export failed with err=%d\n",
>+		       (int)PTR_ERR(dmabuf));
>+		err = PTR_ERR(dmabuf);
>+		goto out;
>+	}
>+
>+	import = i915_gem_prime_import(&i915->drm, dmabuf);
>+	if (IS_ERR(import)) {
>+		pr_err("i915_gem_prime_import failed with err=%d\n",
>+		       (int)PTR_ERR(import));
>+		err = PTR_ERR(import);
>+		goto out_dmabuf;
>+	}
>+
>+	if (import == &obj->base) {
>+		pr_err("i915_gem_prime_import reused gem object!\n");
>+		err = -EINVAL;
>+		goto out_import;
>+	}
>+
>+	import_obj = to_intel_bo(import);
>+
>+	i915_gem_object_lock(import_obj, NULL);
>+	err = ____i915_gem_object_get_pages(import_obj);
>+	if (err) {
>+		pr_err("Different objects dma-buf get_pages failed!\n");
>+		i915_gem_object_unlock(import_obj);
>+		goto out_import;
>+	}
>+
>+	/*
>+	 * If the exported object is not in system memory, something
>+	 * weird is going on. TODO: When p2p is supported, this is no
>+	 * longer considered weird.
>+	 */
>+	if (obj->mm.region != i915->mm.regions[INTEL_REGION_SMEM]) {
>+		pr_err("Exported dma-buf is not in system memory\n");
>+		err = -EINVAL;
>+	}
>+	i915_gem_object_unlock(import_obj);
>+
>+out_import:
>+	i915_gem_object_put(import_obj);
> out_dmabuf:
> 	dma_buf_put(dmabuf);
> out:
> 	i915_gem_object_put(obj);
>+out_ret:
>+	force_different_devices = false;
> 	return err;
> }
>
>@@ -286,6 +362,7 @@ int i915_gem_dmabuf_live_selftests(struct
>drm_i915_private *i915)
> {
> 	static const struct i915_subtest tests[] = {
> 		SUBTEST(igt_dmabuf_export),
>+		SUBTEST(igt_dmabuf_import_same_driver),
> 	};
>
> 	return i915_subtests(tests, i915);
>--
>2.31.1