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

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index ee2a30422020615f8b37cd6e375ac80411e1872d..d699ea3ab80be3d35e40072ec86d0fd40a7924ec 100644 (file)
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2730,6 +2730,9 @@ i915_gem_object_pwrite_gtt(struct drm_i915_gem_object *obj,
        if (i915_gem_object_has_pages(obj))
                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