Patch "drm/i915: Deny wrapping an userptr into a framebuffer" has been added to the 4.2-stable tree

This is a note to let you know that I've just added the patch titled

drm/i915: Deny wrapping an userptr into a framebuffer

to the 4.2-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
drm-i915-deny-wrapping-an-userptr-into-a-framebuffer.patch
and it can be found in the queue-4.2 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Chris Wilson <[email protected]>
Date: Tue, 13 Oct 2015 14:22:26 +0100
Subject: drm/i915: Deny wrapping an userptr into a framebuffer
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From: Chris Wilson <[email protected]>

commit cc917ab43541db3ff66d0136042686d40a1b4c9a upstream.

Pinning a userptr onto the hardware raises interesting questions about the lifetime of such a surface as the framebuffer extends that life beyond the client's address space. That is the hardware will need to keep scanning out from the backing storage even after the client wants to remap its address space. As the hardware pins the backing storage, the userptr becomes invalid and this raises a WARN when the clients tries to unmap its address space. The situation can be even more complicated when the buffer is passed between processes, between a client and display server, where the lifetime and hardware access is even more confusing. Deny it.

---
 drivers/gpu/drm/i915/i915_gem_userptr.c |    5 ++++-
 drivers/gpu/drm/i915/intel_display.c    |    5 +++++
 2 files changed, 9 insertions(+), 1 deletion(-)

@@ -804,7 +804,10 @@ static const struct drm_i915_gem_object_
  * Also note, that the object created here is not currently a "first class"
  * object, in that several ioctls are banned. These are the CPU access
  * ioctls: mmap(), pwrite and pread. In practice, you are expected to use
- * direct access via your pointer rather than use those ioctls.
+ * direct access via your pointer rather than use those ioctls. Another
+ * restriction is that we do not allow userptr surfaces to be pinned to the
+ * hardware and so we reject any attempt to create a framebuffer out of a
+ * userptr.
  *
  * If you think this is a good interface to use to pass GPU memory between
  * drivers, please use dma-buf instead. In fact, wherever possible use

@@ -14072,6 +14072,11 @@ static int intel_user_framebuffer_create
 	struct intel_framebuffer *intel_fb = to_intel_framebuffer(fb);
 	struct drm_i915_gem_object *obj = intel_fb->obj;
 
+	if (obj->userptr.mm) {
+		DRM_DEBUG("attempting to use a userptr for a framebuffer, denied\n");
+		return -EINVAL;
+	}
+
 	return drm_gem_handle_create(file, &obj->base, handle);
 }
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.2/drm-i915-flush-pipecontrol-post-sync-writes.patch queue-4.2/drm-i915-deny-wrapping-an-userptr-into-a-framebuffer.patch