drm/i915: Deny wrapping an userptr into a framebuffer

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: Luis Henriques <luis.henriques@canonical.com>

diff --git a/drivers/gpu/drm/i915/i915_gem_userptr.c b/drivers/gpu/drm/i915/i915_gem_userptr.c
index 7b7a35d71c0857ff6833184ecca1d7ccde5a1bb1..3d98e0d2903d8b6d5ed9b6b35e32624b07e56b52 100644 (file)
--- a/drivers/gpu/drm/i915/i915_gem_userptr.c
+++ b/drivers/gpu/drm/i915/i915_gem_userptr.c
@@ -630,7 +630,10 @@ 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 c7d7dbec49656c45818a91f73d8c4addc0723779..535f11187dccf0377dd3c5c6cab124a22447998a 100644 (file)
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -11285,6 +11285,11 @@ 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);
 }