Re: [PATCH v1 34/36] kfence: drop nth_page() usage
From: Marco Elver <elver@google.com>
Date: 2025-08-28 08:43:54
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 Thu, 28 Aug 2025 at 00:11, 'David Hildenbrand' via kasan-dev [off-list ref] wrote:
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>
Reviewed-by: Marco Elver <elver@google.com> Thanks.
quoted hunk ↗ jump to hunk
--- mm/kfence/core.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-)diff --git a/mm/kfence/core.c b/mm/kfence/core.c index 0ed3be100963a..727c20c94ac59 100644 --- a/mm/kfence/core.c +++ b/mm/kfence/core.c@@ -594,15 +594,14 @@ 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, start_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)); /* * Set up object pages: they must have PGTY_slab set to avoid freeing@@ -613,11 +612,12 @@ static unsigned long kfence_init_pool(void) * enters __slab_free() slow-path. */ for (i = 0; i < KFENCE_POOL_SIZE / PAGE_SIZE; i++) { - struct slab *slab = page_slab(nth_page(pages, i)); + struct slab *slab; if (!i || (i % 2)) continue; + slab = page_slab(pfn_to_page(start_pfn + i)); __folio_set_slab(slab_folio(slab)); #ifdef CONFIG_MEMCG slab->obj_exts = (unsigned long)&kfence_metadata_init[i / 2 - 1].obj_exts |@@ -665,10 +665,12 @@ static unsigned long kfence_init_pool(void) reset_slab: for (i = 0; i < KFENCE_POOL_SIZE / PAGE_SIZE; i++) { - struct slab *slab = page_slab(nth_page(pages, i)); + struct slab *slab; if (!i || (i % 2)) continue; + + slab = page_slab(pfn_to_page(start_pfn + i)); #ifdef CONFIG_MEMCG slab->obj_exts = 0; #endif --2.50.1 -- You received this message because you are subscribed to the Google Groups "kasan-dev" group. To unsubscribe from this group and stop receiving emails from it, send an email to kasan-dev+unsubscribe@googlegroups.com. To view this discussion visit https://groups.google.com/d/msgid/kasan-dev/20250827220141.262669-35-david%40redhat.com.