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

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

[gregkh]

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 <stable@vger.kernel.org> know about it.


>From cc917ab43541db3ff66d0136042686d40a1b4c9a Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris@chris-wilson.co.uk>
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 <chris@chris-wilson.co.uk>

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.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Michał Winiarski <michal.winiarski@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

--- a/drivers/gpu/drm/i915/i915_gem_userptr.c
+++ b/drivers/gpu/drm/i915/i915_gem_userptr.c
@@ -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
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -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 chris@chris-wilson.co.uk 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