drm/fb-helper: Fix clip rectangle height

Computing the clip rectangle is prone to off-by-one errors when writes
happen near the end of a memory page. Point the end of the memory area
to the first trailing byte, so that (end - start) returns the area's
length.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220209161617.3553-2-tzimmermann@suse.de

diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index f15127a..a37fb4a 100644 (file)
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -699,7 +699,7 @@ void drm_fb_helper_deferred_io(struct fb_info *info,
        max = 0;
        list_for_each_entry(page, pagelist, lru) {
                start = page->index << PAGE_SHIFT;
-               end = start + PAGE_SIZE - 1;
+               end = start + PAGE_SIZE;
                min = min(min, start);
                max = max(max, end);
        }