[PATCH 03/12] drm/vmwgfx: clamp dirty-page range with min, not max

[Zack Rusin <zack.rusin@broadcom.com>]

vmw_bo_dirty_transfer_to_res() and vmw_bo_dirty_clear() compute the
intersection of a resource's page range with the BO's tracked dirty
range, but clamp res_end against dirty->end with max() instead of
min().  When dirty->end exceeds the resource end, the loop walks past
the resource's pages, calls vmw_resource_dirty_update() for ranges
owned by other resources sharing the same backing MOB and clears
their pending dirty bits via bitmap_clear().  The result is silent
loss of writeback for unrelated resources whenever two resources
share a MOB.

Use min() in both functions so the loop is bounded to the
intersection of the resource and dirty ranges.

Fixes: b7468b15d271 ("drm/vmwgfx: Implement an infrastructure for write-coherent resources")
Fixes: 965544150d1c ("drm/vmwgfx: Refactor cursor handling")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4.7
Signed-off-by: Zack Rusin <zack.rusin@broadcom.com>
---
 drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c b/drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c
index 45561bc1c9ef..8ab88f388652 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c
@@ -311,7 +311,7 @@ void vmw_bo_dirty_transfer_to_res(struct vmw_resource *res)
 		return;
 
 	cur = max(res_start, dirty->start);
-	res_end = max(res_end, dirty->end);
+	res_end = min(res_end, dirty->end);
 	while (cur < res_end) {
 		unsigned long num;
 
@@ -347,7 +347,7 @@ void vmw_bo_dirty_clear(struct vmw_bo *vbo)
 		return;
 
 	cur = max(res_start, dirty->start);
-	res_end = max(res_end, dirty->end);
+	res_end = min(res_end, dirty->end);
 	while (cur < res_end) {
 		unsigned long num;
 
-- 
2.51.0