Re: [PATCH RFC 23/35] scatterlist: disallow non-contigous page ranges in a single SG entry
From: Marek Szyprowski <m.szyprowski@samsung.com>
Date: 2025-08-22 08:15:21
Also in:
dri-devel, intel-gfx, io-uring, kvm, linux-arm-kernel, linux-crypto, linux-ide, linux-iommu, linux-kselftest, linux-mips, linux-mm, linux-mmc, linux-riscv, linux-s390, linux-scsi, lkml, virtualization
On 21.08.2025 22:06, David Hildenbrand wrote:
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. We can now drop the nth_page() usage in sg_page_iter_page(). Signed-off-by: David Hildenbrand <redacted>
Acked-by: Marek Szyprowski <m.szyprowski@samsung.com>
quoted hunk ↗ jump to hunk
--- include/linux/scatterlist.h | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h index 6f8a4965f9b98..8196949dfc82c 100644 --- a/include/linux/scatterlist.h +++ b/include/linux/scatterlist.h@@ -6,6 +6,7 @@ #include <linux/types.h> #include <linux/bug.h> #include <linux/mm.h> +#include <linux/mm_inline.h> #include <asm/io.h> struct scatterlist {@@ -158,6 +159,7 @@ 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 +602,7 @@ 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; } /**
Best regards -- Marek Szyprowski, PhD Samsung R&D Institute Poland