The patch titled Subject: mm/mprotect: minor can_change_pte_writable() cleanups has been added to the -mm mm-unstable branch. Its filename is mm-mprotect-minor-can_change_pte_writable-cleanups.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-mprotect-minor-can_change_pte_writable-cleanups.patch This patch will later appear in the mm-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days ------------------------------------------------------ From: David Hildenbrand <david@xxxxxxxxxx> Subject: mm/mprotect: minor can_change_pte_writable() cleanups Date: Tue, 8 Nov 2022 18:46:47 +0100 We want to replicate this code for handling PMDs soon. (1) No need to crash the kernel, warning and rejecting is good enough. As this will no longer get optimized out, drop the pte_write() check: no harm would be done. (2) Add a comment why PROT_NONE mapped pages are excluded. (3) Add a comment regarding MAP_SHARED handling and why we rely on the dirty bit in the PTE. Link: https://lkml.kernel.org/r/20221108174652.198904-3-david@xxxxxxxxxx Signed-off-by: David Hildenbrand <david@xxxxxxxxxx> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx> Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx> Cc: Dave Chinner <david@xxxxxxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx> Cc: Mike Rapoport <rppt@xxxxxxxxxx> Cc: Nadav Amit <namit@xxxxxxxxxx> Cc: Nicholas Piggin <npiggin@xxxxxxxxx> Cc: Peter Xu <peterx@xxxxxxxxxx> Cc: Vlastimil Babka <vbabka@xxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/mprotect.c | 19 ++++++++++++++----- 1 file changed, 14 insertions(+), 5 deletions(-) --- a/mm/mprotect.c~mm-mprotect-minor-can_change_pte_writable-cleanups +++ a/mm/mprotect.c @@ -44,8 +44,10 @@ static inline bool can_change_pte_writab { struct page *page; - VM_BUG_ON(!(vma->vm_flags & VM_WRITE) || pte_write(pte)); + if (WARN_ON_ONCE(!(vma->vm_flags & VM_WRITE))) + return false; + /* Don't touch entries that are not even readable. */ if (pte_protnone(pte)) return false; @@ -59,15 +61,22 @@ static inline bool can_change_pte_writab if (!(vma->vm_flags & VM_SHARED)) { /* - * We can only special-case on exclusive anonymous pages, - * because we know that our write-fault handler similarly would - * map them writable without any additional checks while holding - * the PT lock. + * Writable MAP_PRIVATE mapping: We can only special-case on + * exclusive anonymous pages, because we know that our + * write-fault handler similarly would map them writable without + * any additional checks while holding the PT lock. */ page = vm_normal_page(vma, addr, pte); return page && PageAnon(page) && PageAnonExclusive(page); } + /* + * Writable MAP_SHARED mapping: "clean" might indicate that the FS still + * needs a real write-fault for writenotify + * (see vma_wants_writenotify()). If "dirty", the assumption is that the + * FS was already notified and we can simply mark the PTE writable + * just like the write-fault handler would do. + */ return pte_dirty(pte); } _ Patches currently in -mm which might be from david@xxxxxxxxxx are selftests-vm-anon_cow-test-cow-handling-of-anonymous-memory.patch selftests-vm-anon_cow-test-cow-handling-of-anonymous-memory-fix.patch selftests-vm-factor-out-pagemap_is_populated-into-vm_util.patch selftests-vm-anon_cow-thp-tests.patch selftests-vm-anon_cow-hugetlb-tests.patch selftests-vm-anon_cow-add-liburing-test-cases.patch selftests-vm-anon_cow-add-liburing-test-cases-fix.patch mm-gup_test-start-stop-read-functionality-for-pin-longterm-test.patch mm-gup_test-start-stop-read-functionality-for-pin-longterm-test-fix.patch selftests-vm-anon_cow-add-r-o-longterm-tests-via-gup_test.patch selftests-vm-add-ksm-unmerge-tests.patch mm-pagewalk-dont-trigger-test_walk-in-walk_page_vma.patch selftests-vm-add-test-to-measure-madv_unmergeable-performance.patch mm-ksm-simplify-break_ksm-to-not-rely-on-vm_fault_write.patch mm-remove-vm_fault_write.patch mm-ksm-fix-ksm-cow-breaking-with-userfaultfd-wp-via-fault_flag_unshare.patch mm-pagewalk-add-walk_page_range_vma.patch mm-ksm-convert-break_ksm-to-use-walk_page_range_vma.patch mm-gup-remove-foll_migration.patch mm-mprotect-minor-can_change_pte_writable-cleanups.patch mm-huge_memory-try-avoiding-write-faults-when-changing-pmd-protection.patch mm-mprotect-factor-out-check-whether-manual-pte-write-upgrades-are-required.patch mm-autonuma-use-can_change_ptepmd_writable-to-replace-savedwrite.patch mm-remove-unused-savedwrite-infrastructure.patch selftests-vm-anon_cow-add-mprotect-optimization-tests.patch