Messages in this thread Patch in this message | | | From | Nadav Amit <> | Subject | [RFC PATCH 04/14] mm/mprotect: preserve write with MM_CP_TRY_CHANGE_WRITABLE | Date | Mon, 18 Jul 2022 05:02:02 -0700 |
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From: Nadav Amit <namit@vmware.com>
When MM_CP_TRY_CHANGE_WRITABLE is used, change_pte_range() tries to set PTEs as writable.
Yet, writable PTEs might still become read-only, due to various limitations of the logic that determines whether a PTE can become writable (see can_change_pte_writable()). Anyhow, it is much easier to keep the writable bit set when MM_CP_TRY_CHANGE_WRITABLE is used than to first clear it and then figure out whether it can be set again.
Preserve the write-bit when MM_CP_TRY_CHANGE_WRITABLE is used, similarly to the way it is done with NUMA.
Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Andrew Cooper <andrew.cooper3@citrix.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Andy Lutomirski <luto@kernel.org> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: David Hildenbrand <david@redhat.com> Cc: Peter Xu <peterx@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Will Deacon <will@kernel.org> Cc: Yu Zhao <yuzhao@google.com> Cc: Nick Piggin <npiggin@gmail.com> Signed-off-by: Nadav Amit <namit@vmware.com> --- mm/mprotect.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/mm/mprotect.c b/mm/mprotect.c index da5b9bf8204f..92bfb17dcb8a 100644 --- a/mm/mprotect.c +++ b/mm/mprotect.c @@ -84,6 +84,7 @@ static unsigned long change_pte_range(struct mmu_gather *tlb, bool uffd_wp = cp_flags & MM_CP_UFFD_WP; bool uffd_wp_resolve = cp_flags & MM_CP_UFFD_WP_RESOLVE; bool will_need = cp_flags & MM_CP_WILL_NEED; + bool try_change_writable = cp_flags & MM_CP_TRY_CHANGE_WRITABLE; tlb_change_page_size(tlb, PAGE_SIZE); @@ -114,7 +115,8 @@ static unsigned long change_pte_range(struct mmu_gather *tlb, oldpte = *pte; if (pte_present(oldpte)) { pte_t ptent; - bool preserve_write = prot_numa && pte_write(oldpte); + bool preserve_write = (prot_numa || try_change_writable) && + pte_write(oldpte); /* * Avoid trapping faults against the zero or KSM @@ -190,8 +192,7 @@ static unsigned long change_pte_range(struct mmu_gather *tlb, * example, if a PTE is already dirty and no other * COW or special handling is required. */ - if ((cp_flags & MM_CP_TRY_CHANGE_WRITABLE) && - !pte_write(ptent) && + if (try_change_writable && !pte_write(ptent) && can_change_pte_writable(vma, addr, ptent)) { ptent = pte_mkwrite(ptent); if (will_need) -- 2.25.1
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