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51 lines
1.7 KiB
Diff
51 lines
1.7 KiB
Diff
diff --git a/include/linux/mm.h b/include/linux/mm.h
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index 79aa518c16a3..5676a670429e 100644
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--- a/include/linux/mm.h
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+++ b/include/linux/mm.h
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@@ -1749,6 +1749,7 @@ static inline struct page *follow_page(struct vm_area_struct *vma,
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#define FOLL_HWPOISON 0x100 /* check page is hwpoisoned */
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#define FOLL_NUMA 0x200 /* force NUMA hinting page fault */
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#define FOLL_MIGRATION 0x400 /* wait for page to replace migration entry */
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+#define FOLL_COW 0x4000 /* internal GUP flag */
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typedef int (*pte_fn_t)(pte_t *pte, pgtable_t token, unsigned long addr,
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void *data);
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diff --git a/mm/memory.c b/mm/memory.c
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index 61926356c09a..a0c9c6cb59d1 100644
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--- a/mm/memory.c
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+++ b/mm/memory.c
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@@ -1441,6 +1441,16 @@ int zap_vma_ptes(struct vm_area_struct *vma, unsigned long address,
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}
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EXPORT_SYMBOL_GPL(zap_vma_ptes);
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+/*
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+ * FOLL_FORCE can write to even unwritable pte's, but only
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+ * after we've gone through a COW cycle and they are dirty.
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+ */
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+static inline bool can_follow_write_pte(pte_t pte, unsigned int flags)
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+{
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+ return pte_write(pte) ||
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+ ((flags & FOLL_FORCE) && (flags & FOLL_COW) && pte_dirty(pte));
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+}
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+
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/**
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* follow_page_mask - look up a page descriptor from a user-virtual address
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* @vma: vm_area_struct mapping @address
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@@ -1550,7 +1560,7 @@ split_fallthrough:
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}
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if ((flags & FOLL_NUMA) && pte_numa(pte))
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goto no_page;
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- if ((flags & FOLL_WRITE) && !pte_write(pte))
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+ if ((flags & FOLL_WRITE) && !can_follow_write_pte(pte, flags))
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goto unlock;
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page = vm_normal_page(vma, address, pte);
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@@ -1858,7 +1868,7 @@ long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
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*/
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if ((ret & VM_FAULT_WRITE) &&
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!(vma->vm_flags & VM_WRITE))
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- foll_flags &= ~FOLL_WRITE;
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+ foll_flags |= FOLL_COW;
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cond_resched();
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}
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