[PATCH] drm/i915/gem: Fix phys BO pread/pwrite with offset

[Joonas Lahtinen <joonas.lahtinen@linux.intel.com>]

sg_page() returns struct page pointer not (void *) so the scaling
of pread/pwrite is wrong for phys BO and wrong parts of BO would be
accessed if non-zero offset is used.

Last impacted platform with overlay or cursor planes using phys
mapping was Gen3/945G/Lakeport.

Reported-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Fixes: c6790dc22312 ("drm/i915: Wean off drm_pci_alloc/drm_pci_free")
Cc: <stable@vger.kernel.org> # v4.5+
Cc: Tvrtko Ursulin <tursulin@ursulin.net>
Cc: Simona Vetter <simona@ffwll.ch>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
---
 drivers/gpu/drm/i915/gem/i915_gem_phys.c | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_phys.c b/drivers/gpu/drm/i915/gem/i915_gem_phys.c
index e375afbf458e..d53129eb5603 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_phys.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_phys.c
@@ -18,6 +18,17 @@
 #include "i915_gem_tiling.h"
 #include "i915_scatterlist.h"
 
+/* Abuse scatterlist to store pointer instead of struct page. */
+static inline void __set_phys_vaddr(struct scatterlist *sg, void *vaddr)
+{
+	sg_assign_page(sg, (struct page *)vaddr);
+}
+
+static inline void *__get_phys_vaddr(struct scatterlist *sg)
+{
+	return (void *)sg_page(sg);
+}
+
 static int i915_gem_object_get_pages_phys(struct drm_i915_gem_object *obj)
 {
 	struct address_space *mapping = obj->base.filp->f_mapping;
@@ -58,7 +69,7 @@ static int i915_gem_object_get_pages_phys(struct drm_i915_gem_object *obj)
 	sg->offset = 0;
 	sg->length = obj->base.size;
 
-	sg_assign_page(sg, (struct page *)vaddr);
+	__set_phys_vaddr(sg, vaddr);
 	sg_dma_address(sg) = dma;
 	sg_dma_len(sg) = obj->base.size;
 
@@ -99,7 +110,7 @@ i915_gem_object_put_pages_phys(struct drm_i915_gem_object *obj,
 			       struct sg_table *pages)
 {
 	dma_addr_t dma = sg_dma_address(pages->sgl);
-	void *vaddr = sg_page(pages->sgl);
+	void *vaddr = __get_phys_vaddr(pages->sgl);
 
 	__i915_gem_object_release_shmem(obj, pages, false);
 
@@ -139,7 +150,7 @@ i915_gem_object_put_pages_phys(struct drm_i915_gem_object *obj,
 int i915_gem_object_pwrite_phys(struct drm_i915_gem_object *obj,
 				const struct drm_i915_gem_pwrite *args)
 {
-	void *vaddr = sg_page(obj->mm.pages->sgl) + args->offset;
+	void *vaddr = __get_phys_vaddr(obj->mm.pages->sgl) + args->offset;
 	char __user *user_data = u64_to_user_ptr(args->data_ptr);
 	struct drm_i915_private *i915 = to_i915(obj->base.dev);
 	int err;
@@ -170,7 +181,7 @@ int i915_gem_object_pwrite_phys(struct drm_i915_gem_object *obj,
 int i915_gem_object_pread_phys(struct drm_i915_gem_object *obj,
 			       const struct drm_i915_gem_pread *args)
 {
-	void *vaddr = sg_page(obj->mm.pages->sgl) + args->offset;
+	void *vaddr = __get_phys_vaddr(obj->mm.pages->sgl) + args->offset;
 	char __user *user_data = u64_to_user_ptr(args->data_ptr);
 	int err;
 
-- 
2.54.0