[PATCH RFC 33/35] kfence: drop nth_page() usage
From: David Hildenbrand <hidden>
Date: 2025-08-21 20:08:43
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
Subsystem:
kfence, memory management, the rest · Maintainers:
Alexander Potapenko, Marco Elver, Andrew Morton, Linus Torvalds
We want to get rid of nth_page(), and kfence init code is the last user. Unfortunately, we might actually walk a PFN range where the pages are not contiguous, because we might be allocating an area from memblock that could span memory sections in problematic kernel configs (SPARSEMEM without SPARSEMEM_VMEMMAP). We could check whether the page range is contiguous using page_range_contiguous() and failing kfence init, or making kfence incompatible these problemtic kernel configs. Let's keep it simple and simply use pfn_to_page() by iterating PFNs. Cc: Alexander Potapenko <glider@google.com> Cc: Marco Elver <elver@google.com> Cc: Dmitry Vyukov <dvyukov@google.com> Signed-off-by: David Hildenbrand <redacted> --- mm/kfence/core.c | 17 ++++++++++------- 1 file changed, 10 insertions(+), 7 deletions(-)
diff --git a/mm/kfence/core.c b/mm/kfence/core.c
index 0ed3be100963a..793507c77f9e8 100644
--- a/mm/kfence/core.c
+++ b/mm/kfence/core.c@@ -594,15 +594,15 @@ static void rcu_guarded_free(struct rcu_head *h) */ static unsigned long kfence_init_pool(void) { - unsigned long addr; - struct page *pages; + unsigned long addr, pfn, start_pfn, end_pfn; int i; if (!arch_kfence_init_pool()) return (unsigned long)__kfence_pool; addr = (unsigned long)__kfence_pool; - pages = virt_to_page(__kfence_pool); + start_pfn = PHYS_PFN(virt_to_phys(__kfence_pool)); + end_pfn = start_pfn + KFENCE_POOL_SIZE / PAGE_SIZE; /* * Set up object pages: they must have PGTY_slab set to avoid freeing
@@ -612,12 +612,13 @@ static unsigned long kfence_init_pool(void) * fast-path in SLUB, and therefore need to ensure kfree() correctly * enters __slab_free() slow-path. */ - for (i = 0; i < KFENCE_POOL_SIZE / PAGE_SIZE; i++) { - struct slab *slab = page_slab(nth_page(pages, i)); + for (pfn = start_pfn; pfn != end_pfn; pfn++) { + struct slab *slab; if (!i || (i % 2)) continue; + slab = page_slab(pfn_to_page(pfn)); __folio_set_slab(slab_folio(slab)); #ifdef CONFIG_MEMCG slab->obj_exts = (unsigned long)&kfence_metadata_init[i / 2 - 1].obj_exts |
@@ -664,11 +665,13 @@ static unsigned long kfence_init_pool(void) return 0; reset_slab: - for (i = 0; i < KFENCE_POOL_SIZE / PAGE_SIZE; i++) { - struct slab *slab = page_slab(nth_page(pages, i)); + for (pfn = start_pfn; pfn != end_pfn; pfn++) { + struct slab *slab; if (!i || (i % 2)) continue; + + slab = page_slab(pfn_to_page(pfn)); #ifdef CONFIG_MEMCG slab->obj_exts = 0; #endif
--
2.50.1