Re: [PATCH v1 11/11] mm/memory: ignore writable bit in folio_pte_batch()
From: Ryan Roberts <ryan.roberts@arm.com>
Date: 2024-01-23 12:35:13
Also in:
linux-arm-kernel, linux-riscv, linux-s390, linuxppc-dev, lkml, sparclinux
On 22/01/2024 19:42, David Hildenbrand wrote:
... and conditionally return to the caller if any pte except the first one is writable. fork() has to make sure to properly write-protect in case any PTE is writable. Other users (e.g., page unmaping) won't care. Signed-off-by: David Hildenbrand <redacted>
Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
quoted hunk ↗ jump to hunk
--- mm/memory.c | 26 +++++++++++++++++++++----- 1 file changed, 21 insertions(+), 5 deletions(-)diff --git a/mm/memory.c b/mm/memory.c index 341b2be845b6e..a26fd0669016b 100644 --- a/mm/memory.c +++ b/mm/memory.c@@ -955,7 +955,7 @@ static __always_inline void __copy_present_ptes(struct vm_area_struct *dst_vma, static inline pte_t __pte_batch_clear_ignored(pte_t pte) { - return pte_clear_soft_dirty(pte_mkclean(pte_mkold(pte))); + return pte_wrprotect(pte_clear_soft_dirty(pte_mkclean(pte_mkold(pte)))); } /*@@ -963,20 +963,29 @@ static inline pte_t __pte_batch_clear_ignored(pte_t pte) * pages of the same folio. * * All PTEs inside a PTE batch have the same PTE bits set, excluding the PFN. - * the accessed bit, dirty bit and soft-dirty bit. + * the accessed bit, dirty bit, soft-dirty bit and writable bit. + . If "any_writable" is set, it will indicate if any other PTE besides the + * first (given) PTE is writable. */ static inline int folio_pte_batch(struct folio *folio, unsigned long addr, - pte_t *start_ptep, pte_t pte, int max_nr) + pte_t *start_ptep, pte_t pte, int max_nr, bool *any_writable) { unsigned long folio_end_pfn = folio_pfn(folio) + folio_nr_pages(folio); const pte_t *end_ptep = start_ptep + max_nr; pte_t expected_pte = __pte_batch_clear_ignored(pte_next_pfn(pte)); pte_t *ptep = start_ptep + 1; + bool writable; + + if (any_writable) + *any_writable = false; VM_WARN_ON_FOLIO(!pte_present(pte), folio); while (ptep != end_ptep) { - pte = __pte_batch_clear_ignored(ptep_get(ptep)); + pte = ptep_get(ptep); + if (any_writable) + writable = !!pte_write(pte); + pte = __pte_batch_clear_ignored(pte); if (!pte_same(pte, expected_pte)) break;@@ -989,6 +998,9 @@ static inline int folio_pte_batch(struct folio *folio, unsigned long addr, if (pte_pfn(pte) == folio_end_pfn) break; + if (any_writable) + *any_writable |= writable; + expected_pte = pte_next_pfn(expected_pte); ptep++; }@@ -1010,6 +1022,7 @@ copy_present_ptes(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma { struct page *page; struct folio *folio; + bool any_writable; int err, nr; page = vm_normal_page(src_vma, addr, pte);@@ -1024,7 +1037,8 @@ copy_present_ptes(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma * by keeping the batching logic separate. */ if (unlikely(!*prealloc && folio_test_large(folio) && max_nr != 1)) { - nr = folio_pte_batch(folio, addr, src_pte, pte, max_nr); + nr = folio_pte_batch(folio, addr, src_pte, pte, max_nr, + &any_writable); if (folio_test_anon(folio)) { folio_ref_add(folio, nr); if (unlikely(folio_try_dup_anon_rmap_ptes(folio, page,@@ -1039,6 +1053,8 @@ copy_present_ptes(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma folio_dup_file_rmap_ptes(folio, page, nr); rss[mm_counter_file(page)] += nr; } + if (any_writable) + pte = pte_mkwrite(pte, src_vma); __copy_present_ptes(dst_vma, src_vma, dst_pte, src_pte, pte, addr, nr); return nr;