Re: [PATCH 12/27] drm/i915/gem: Disallow creating contexts with too many engines

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On 03/05/2021 16:57, Jason Ekstrand wrote:
There's no sense in allowing userspace to create more engines than it
can possibly access via execbuf.

Signed-off-by: Jason Ekstrand <jason@xxxxxxxxxxxxxx>
Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>

FWIW, again for the record, my advice is not to land this one. It makes no sense and it is actively disruptive for no benefit.

Regards,

Tvrtko

---
  drivers/gpu/drm/i915/gem/i915_gem_context.c | 8 ++++----
  1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c
index be42dc918ef6f..8e254d83d65f2 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c
@@ -1640,11 +1640,11 @@ set_engines(struct i915_gem_context *ctx,
  		return -EINVAL;
  	}
- /*
-	 * Note that I915_EXEC_RING_MASK limits execbuf to only using the
-	 * first 64 engines defined here.
-	 */
  	num_engines = (args->size - sizeof(*user)) / sizeof(*user->engines);
+	/* RING_MASK has no shift so we can use it directly here */
+	if (num_engines > I915_EXEC_RING_MASK + 1)
+		return -EINVAL;
+
  	set.engines = alloc_engines(num_engines);
  	if (!set.engines)
  		return -ENOMEM;

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