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authorKrzysztof Karas <krzysztof.karas@intel.com>2024-11-18 12:19:22 +0000
committerAndi Shyti <andi.shyti@linux.intel.com>2024-12-05 14:29:48 +0100
commit2e0438f9c3d25eea8bc8e9b4dcff7edfb64cb9e7 (patch)
tree95596a32961f26277ce7ff5bf96df0f131e1204b /drivers
parentb939a08bc378a7c716ad7a9486b48794b95d22f5 (diff)
drm/i915: ensure segment offset never exceeds allowed max
Commit 255fc1703e42 ("drm/i915/gem: Calculate object page offset for partial memory mapping") introduced a new offset, which accounts for userspace mapping not starting from the beginning of object's scatterlist. This works fine for cases where first object pte is larger than the new offset - "r->sgt.curr" counter is set to the offset to match the difference in the number of total pages. However, if object's first pte's size is equal to or smaller than the offset, then information about the offset in userspace is covered up by moving "r->sgt" pointer in remap_sg(): r->sgt.curr += PAGE_SIZE; if (r->sgt.curr >= r->sgt.max) r->sgt = __sgt_iter(__sg_next(r->sgt.sgp), use_dma(r->iobase)); This means that two or more pages from virtual memory are counted for only one page in object's memory, because after moving "r->sgt" pointer "r->sgt.curr" will be 0. We should account for this mismatch by moving "r->sgt" pointer to the next pte. For that we may use "r.sgt.max", which already holds the max allowed size. This change also eliminates possible confusion, when looking at i915_scatterlist.h and remap_io_sg() code: former has scatterlist pointer definition, which differentiates "s.max" value based on "dma" flag (sg_dma_len() is used only when the flag is enabled), while latter uses sg_dma_len() indiscriminately. This patch aims to resolve issue: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/12031 v3: - instead of checking if r.sgt.curr would exceed allowed max, changed the value in the while loop to be aligned with `dma` value v4: - remove unnecessary parent relation v5: - update commit message with explanation about page counting mismatch and link to the issue Signed-off-by: Krzysztof Karas <krzysztof.karas@intel.com> Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com> Signed-off-by: Andi Shyti <andi.shyti@linux.intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/upbjdavlbcxku63ns4vstp5kgbn2anxwewpmnppszgb67fn66t@tfclfgkqijue
Diffstat (limited to 'drivers')
-rw-r--r--drivers/gpu/drm/i915/i915_mm.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/drivers/gpu/drm/i915/i915_mm.c b/drivers/gpu/drm/i915/i915_mm.c
index f5c97a620962..76e2801619f0 100644
--- a/drivers/gpu/drm/i915/i915_mm.c
+++ b/drivers/gpu/drm/i915/i915_mm.c
@@ -143,8 +143,8 @@ int remap_io_sg(struct vm_area_struct *vma,
/* We rely on prevalidation of the io-mapping to skip track_pfn(). */
GEM_BUG_ON((vma->vm_flags & EXPECTED_FLAGS) != EXPECTED_FLAGS);
- while (offset >= sg_dma_len(r.sgt.sgp) >> PAGE_SHIFT) {
- offset -= sg_dma_len(r.sgt.sgp) >> PAGE_SHIFT;
+ while (offset >= r.sgt.max >> PAGE_SHIFT) {
+ offset -= r.sgt.max >> PAGE_SHIFT;
r.sgt = __sgt_iter(__sg_next(r.sgt.sgp), use_dma(iobase));
if (!r.sgt.sgp)
return -EINVAL;