Provide a helper function for finishing write faults due to PTE being read-only. The helper will be used by DAX to avoid the need of complicating generic MM code with DAX locking specifics.
Signed-off-by: Jan Kara <[email protected]> --- include/linux/mm.h | 1 + mm/memory.c | 62 +++++++++++++++++++++++++++++++++++------------------- 2 files changed, 41 insertions(+), 22 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index daf690fccc0c..32ff572a6e6c 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -601,6 +601,7 @@ static inline pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma) void do_set_pte(struct vm_area_struct *vma, unsigned long address, struct page *page, pte_t *pte, bool write, bool anon); int finish_fault(struct vm_area_struct *vma, struct vm_fault *vmf); +int finish_mkwrite_fault(struct vm_area_struct *vma, struct vm_fault *vmf); #endif /* diff --git a/mm/memory.c b/mm/memory.c index 1d2916c53d43..30cf7b36df48 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -2262,6 +2262,41 @@ oom: return VM_FAULT_OOM; } +/** + * finish_mkrite_fault - finish page fault making PTE writeable once the page + * page is prepared + * + * @vma: virtual memory area + * @vmf: structure describing the fault + * + * This function handles all that is needed to finish a write page fault due + * to PTE being read-only once the mapped page is prepared. It handles locking + * of PTE and modifying it. The function returns 0 on success, error in case + * the PTE changed before we acquired PTE lock. + * + * The function expects the page to be locked or other protection against + * concurrent faults / writeback (such as DAX radix tree locks). + */ +int finish_mkwrite_fault(struct vm_area_struct *vma, struct vm_fault *vmf) +{ + unsigned long address = (unsigned long)vmf->virtual_address; + pte_t *pte; + spinlock_t *ptl; + + pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, address, &ptl); + /* + * We might have raced with another page fault while we + * released the pte_offset_map_lock. + */ + if (!pte_same(*pte, vmf->orig_pte)) { + pte_unmap_unlock(pte, ptl); + return -EBUSY; + } + wp_page_reuse(vma->vm_mm, vma, address, pte, ptl, vmf->orig_pte, + vmf->page); + return 0; +} + /* * Handle write page faults for VM_MIXEDMAP or VM_PFNMAP for a VM_SHARED * mapping @@ -2282,17 +2317,12 @@ static int wp_pfn_shared(struct mm_struct *mm, ret = vma->vm_ops->pfn_mkwrite(vma, &vmf); if (ret & VM_FAULT_ERROR) return ret; - page_table = pte_offset_map_lock(mm, pmd, address, &ptl); - /* - * We might have raced with another page fault while we - * released the pte_offset_map_lock. - */ - if (!pte_same(*page_table, orig_pte)) { - pte_unmap_unlock(page_table, ptl); + if (finish_mkwrite_fault(vma, &vmf) < 0) return 0; - } + } else { + wp_page_reuse(mm, vma, address, page_table, ptl, orig_pte, + NULL); } - wp_page_reuse(mm, vma, address, page_table, ptl, orig_pte, NULL); return VM_FAULT_WRITE; } @@ -2319,28 +2349,16 @@ static int wp_page_shared(struct mm_struct *mm, struct vm_area_struct *vma, put_page(old_page); return tmp; } - /* - * Since we dropped the lock we need to revalidate - * the PTE as someone else may have changed it. If - * they did, we just return, as we can count on the - * MMU to tell us if they didn't also make it writable. - */ - page_table = pte_offset_map_lock(mm, pmd, address, - &ptl); - if (!pte_same(*page_table, orig_pte)) { + if (finish_mkwrite_fault(vma, &vmf) < 0) { unlock_page(old_page); - pte_unmap_unlock(page_table, ptl); put_page(old_page); return 0; } - wp_page_reuse(mm, vma, address, page_table, ptl, orig_pte, - old_page); } else { wp_page_reuse(mm, vma, address, page_table, ptl, orig_pte, old_page); lock_page(old_page); } - fault_dirty_shared_page(vma, old_page); put_page(old_page); return VM_FAULT_WRITE; -- 2.6.6 _______________________________________________ Linux-nvdimm mailing list [email protected] https://lists.01.org/mailman/listinfo/linux-nvdimm
