The expectation is that there is currently no user that would pass in
non-contigous page ranges: no allocator, not even VMA, will hand these
out.
The only problematic part would be if someone would provide a range
obtained directly from memblock, or manually merge problematic ranges.
If we find such cases, we should fix them to create separate
SG entries.
Let's check in sg_set_page() that this is really the case. No need to
check in sg_set_folio(), as pages in a folio are guaranteed to be
contiguous. As sg_set_page() gets inlined into modules, we have to
export the page_range_contiguous() helper -- use EXPORT_SYMBOL, there is
nothing special about this helper such that we would want to enforce
GPL-only modules.
We can now drop the nth_page() usage in sg_page_iter_page().
Acked-by: Marek Szyprowski <m.szyprow...@samsung.com>
Signed-off-by: David Hildenbrand <da...@redhat.com>
---
include/linux/scatterlist.h | 3 ++-
mm/util.c | 1 +
2 files changed, 3 insertions(+), 1 deletion(-)
diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
index 6f8a4965f9b98..29f6ceb98d74b 100644
--- a/include/linux/scatterlist.h
+++ b/include/linux/scatterlist.h
@@ -158,6 +158,7 @@ static inline void sg_assign_page(struct scatterlist *sg,
struct page *page)
static inline void sg_set_page(struct scatterlist *sg, struct page *page,
unsigned int len, unsigned int offset)
{
+ VM_WARN_ON_ONCE(!page_range_contiguous(page, ALIGN(len + offset,
PAGE_SIZE) / PAGE_SIZE));
sg_assign_page(sg, page);
sg->offset = offset;
sg->length = len;
@@ -600,7 +601,7 @@ void __sg_page_iter_start(struct sg_page_iter *piter,
*/
static inline struct page *sg_page_iter_page(struct sg_page_iter *piter)
{
- return nth_page(sg_page(piter->sg), piter->sg_pgoffset);
+ return sg_page(piter->sg) + piter->sg_pgoffset;
}
/**
diff --git a/mm/util.c b/mm/util.c
index 0bf349b19b652..e8b9da6b13230 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -1312,5 +1312,6 @@ bool page_range_contiguous(const struct page *page,
unsigned long nr_pages)
return false;
return true;
}
+EXPORT_SYMBOL(page_range_contiguous);
#endif
#endif /* CONFIG_MMU */
--
2.50.1
