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mm: remove gup_flags FOLL_WRITE games from __get_user_pages() #29

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mm: remove gup_flags FOLL_WRITE games from __get_user_pages() #29

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1 change: 1 addition & 0 deletions include/linux/mm.h
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Original file line number Diff line number Diff line change
Expand Up @@ -1954,6 +1954,7 @@ static inline struct page *follow_page(struct vm_area_struct *vma,
#define FOLL_HWPOISON 0x100 /* check page is hwpoisoned */
#define FOLL_NUMA 0x200 /* force NUMA hinting page fault */
#define FOLL_MIGRATION 0x400 /* wait for page to replace migration entry */
#define FOLL_COW 0x4000 /* internal GUP flag */

typedef int (*pte_fn_t)(pte_t *pte, pgtable_t token, unsigned long addr,
void *data);
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14 changes: 12 additions & 2 deletions mm/memory.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1441,6 +1441,16 @@ int zap_vma_ptes(struct vm_area_struct *vma, unsigned long address,
}
EXPORT_SYMBOL_GPL(zap_vma_ptes);

/*
* FOLL_FORCE can write to even unwritable pte's, but only
* after we've gone through a COW cycle and they are dirty.
*/
static inline bool can_follow_write_pte(pte_t pte, unsigned int flags)
{
return pte_write(pte) ||
((flags & FOLL_FORCE) && (flags & FOLL_COW) && pte_dirty(pte));
}

/**
* follow_page_mask - look up a page descriptor from a user-virtual address
* @vma: vm_area_struct mapping @address
Expand Down Expand Up @@ -1561,7 +1571,7 @@ struct page *follow_page_mask(struct vm_area_struct *vma,
}
if ((flags & FOLL_NUMA) && pte_numa(pte))
goto no_page;
if ((flags & FOLL_WRITE) && !pte_write(pte))
if ((flags & FOLL_WRITE) && !can_follow_write_pte(pte, flags))
goto unlock;

page = vm_normal_page(vma, address, pte);
Expand Down Expand Up @@ -1869,7 +1879,7 @@ long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
*/
if ((ret & VM_FAULT_WRITE) &&
!(vma->vm_flags & VM_WRITE))
foll_flags &= ~FOLL_WRITE;
foll_flags |= FOLL_COW;

cond_resched();
}
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