On Mon, Jun 28, 2021 at 07:45:31PM +0000, Ruhl, Michael J wrote:
> >-----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.
Hm I'm not sure this is the best interface abuse, since if we combine this
with amdgpu it goes boom. Also I thought the dynamic stuff is optional (or
is that only for the importer).
What I discussed a bit with Maarten on irc is to essentially emulate the
rules of what a dynamic exporter would end up with with a non-dynamic
importer: pin/unpin the buffer at attach/detach time. We could fake this
in our attach/detach callbacks.
At least I don't think it's the locking changes that saves us here, but
the caching of the sgt list in attach/detach. As long as we hand-roll that
we should be fine. So hand-rolling that feels like the best option to make
sure we're not making this worse, as long as we haven't fully validated
the true dynamic importer _and_ exporter case.
Cheers, Daniel
> 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
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
