If the IOMMU supports pages smaller than the CPU page size, segments
which lie at offsets within the CPU page may be mapped based on the
finer-grained IOMMU page boundaries. This minimises the amount of
non-buffer memory between the CPU page boundary and the start of the
segment which must be mapped and therefore exposed to the device, and
brings the default iommu_map_sg implementation in line with
iommu_map/unmap with respect to alignment.
Signed-off-by: Robin Murphy <robin.mur...@arm.com>
---
Hi Joerg,
I noticed this whilst wiring up DMA mapping to this new API - on arm64
we anticipate running 4k IOMMU pages with 64k CPU pages, in which case
the alignment check ends up being unnecessarily strict.
Regards,
Robin.
drivers/iommu/iommu.c | 18 ++++++++++++++----
1 file changed, 14 insertions(+), 4 deletions(-)
diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 08c53c5..5c4101a 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -1129,14 +1129,24 @@ size_t default_iommu_map_sg(struct iommu_domain
*domain, unsigned long iova,
{
struct scatterlist *s;
size_t mapped = 0;
- unsigned int i;
+ unsigned int i, min_pagesz;
int ret;
+ if (unlikely(domain->ops->pgsize_bitmap == 0UL))
+ return 0;
+
+ min_pagesz = 1 << __ffs(domain->ops->pgsize_bitmap);
+
for_each_sg(sg, s, nents, i) {
- phys_addr_t phys = page_to_phys(sg_page(s));
+ phys_addr_t phys = page_to_phys(sg_page(s)) + s->offset;
- /* We are mapping on page boundarys, so offset must be 0 */
- if (s->offset)
+ /*
+ * We are mapping on IOMMU page boundaries, so offset within
+ * the page must be 0. However, the IOMMU may support pages
+ * smaller than PAGE_SIZE, so s->offset may still represent
+ * an offset of that boundary within the CPU page.
+ */
+ if (!IS_ALIGNED(s->offset, min_pagesz))
goto out_err;
ret = iommu_map(domain, iova + mapped, phys, s->length, prot);
--
1.9.1
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