>-----Original Message-----
>From: Thomas Hellström <thomas.hellst...@linux.intel.com>
>Sent: Monday, June 28, 2021 10:46 AM
>To: intel-...@lists.freedesktop.org; dri-devel@lists.freedesktop.org
>Cc: Auld, Matthew <matthew.a...@intel.com>;
>maarten.lankho...@linux.intel.com; Thomas Hellström
><thomas.hellst...@linux.intel.com>; Ruhl; Ruhl, Michael J
><michael.j.r...@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.r...@intel.com>

Mike

>Reported-by: Ruhl, Michael J <michael.j.r...@intel.com>
>Cc: Ruhl, Michael J <michael.j.r...@intel.com>
>Signed-off-by: Thomas Hellström <thomas.hellst...@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

Reply via email to