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kfence: drop nth_page() usage 

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.

Link: https://lkml.kernel.org/r/20250901150359.867252-36-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Marco Elver <elver@google.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
David Hildenbrand 2025-09-01 17:03:56 +02:00 committed by Andrew Morton
parent b5ba761a7f
commit 56531761d4
1 changed files with 7 additions and 5 deletions
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12
mm/kfence/core.c
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@ -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