drm/i915: Report -EFAULT before pwrite fast path into shmemfs

When pwriting into shmemfs, the fast path pagecache_write does not
notice when it is writing to beyond the end of the truncated shmemfs
inode. Report -EFAULT directly when we try to use pwrite into the
!I915_MADV_WILLNEED object.

Fixes: 7c55e2c5772d ("drm/i915: Use pagecache write to prepopulate shmemfs from pwrite-ioctl")
Testcase: igt/gem_madvise/dontneed-before-pwrite
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Matthew Auld <matthew.william.auld@gmail.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171016202732.25459-1-chris@chris-wilson.co.uk
(cherry picked from commit a6d65e451cc4e7127698384868a4447ee7be7d16)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index af289d35b77a..32e857dc507c 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2657,6 +2657,9 @@ i915_gem_object_pwrite_gtt(struct drm_i915_gem_object *obj,
         if (READ_ONCE(obj->mm.pages))
                 return -ENODEV;
 
+        if (obj->mm.madv != I915_MADV_WILLNEED)
+                return -EFAULT;
+
         /* Before the pages are instantiated the object is treated as being
          * in the CPU domain. The pages will be clflushed as required before
          * use, and we can freely write into the pages directly. If userspace