[3.19.y-ckt stable] Patch "drm/i915: Deny wrapping an userptr into a framebuffer" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    drm/i915: Deny wrapping an userptr into a framebuffer

to the linux-3.19.y-queue branch of the 3.19.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.19.y-queue

This patch is scheduled to be released in version 3.19.8-ckt10.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.19.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From ae517cf78558d8b484b7026366e1d936e43a93c5 Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris at chris-wilson.co.uk>
Date: Tue, 13 Oct 2015 14:22:26 +0100
Subject: [PATCH 078/120] drm/i915: Deny wrapping an userptr into a framebuffer
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

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 at chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
Cc: Michał Winiarski <michal.winiarski at intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
Signed-off-by: Jani Nikula <jani.nikula at intel.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/gpu/drm/i915/i915_gem_userptr.c | 5 ++++-
 drivers/gpu/drm/i915/intel_display.c    | 5 +++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_userptr.c b/drivers/gpu/drm/i915/i915_gem_userptr.c
index 1719078..ce175d0 100644
--- a/drivers/gpu/drm/i915/i915_gem_userptr.c
+++ b/drivers/gpu/drm/i915/i915_gem_userptr.c
@@ -776,7 +776,10 @@ static const struct drm_i915_gem_object_ops i915_gem_userptr_ops = {
  * 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
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index a67dde0..66adee1 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -12595,6 +12595,11 @@ static int intel_user_framebuffer_create_handle(struct drm_framebuffer *fb,
 	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);
 }

--
1.9.1