Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 66a6197c authored by Jan Kara's avatar Jan Kara Committed by Linus Torvalds
Browse files

mm: provide helper for finishing mkwrite faults 

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.

Link: http://lkml.kernel.org/r/1479460644-25076-16-git-send-email-jack@suse.cz


Signed-off-by: default avatarJan Kara <jack@suse.cz>
Reviewed-by: default avatarRoss Zwisler <ross.zwisler@linux.intel.com>
Acked-by: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 997dd98d

include/linux/mm.h

+1 −0
Original line number Diff line number Diff line
@@ -615,6 +615,7 @@ static inline pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma) 
int alloc_set_pte(struct vm_fault *vmf, struct mem_cgroup *memcg,

		struct page *page);

int finish_fault(struct vm_fault *vmf);

int finish_mkwrite_fault(struct vm_fault *vmf);

#endif



/*

mm/memory.c

+40 −27
Original line number Diff line number Diff line
@@ -2269,6 +2269,38 @@ static int wp_page_copy(struct vm_fault *vmf) 
	return VM_FAULT_OOM;

}



/**

 * finish_mkwrite_fault - finish page fault for a shared mapping, making PTE

 *			  writeable once the page is prepared

 *

 * @vmf: structure describing the fault

 *

 * This function handles all that is needed to finish a write page fault in a

 * shared mapping due to PTE being read-only once the mapped page is prepared.

 * It handles locking of PTE and modifying it. The function returns

 * VM_FAULT_WRITE on success, 0 when PTE got 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_fault *vmf)

{

	WARN_ON_ONCE(!(vmf->vma->vm_flags & VM_SHARED));

	vmf->pte = pte_offset_map_lock(vmf->vma->vm_mm, vmf->pmd, vmf->address,

				       &vmf->ptl);

	/*

	 * We might have raced with another page fault while we released the

	 * pte_offset_map_lock.

	 */

	if (!pte_same(*vmf->pte, vmf->orig_pte)) {

		pte_unmap_unlock(vmf->pte, vmf->ptl);

		return 0;

	}

	wp_page_reuse(vmf);

	return VM_FAULT_WRITE;

}



/*

 * Handle write page faults for VM_MIXEDMAP or VM_PFNMAP for a VM_SHARED

 * mapping
@@ -2285,16 +2317,7 @@ static int wp_pfn_shared(struct vm_fault *vmf) 
		ret = vma->vm_ops->pfn_mkwrite(vma, vmf);

		if (ret & VM_FAULT_ERROR)

			return ret;

		vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd,

				vmf->address, &vmf->ptl);

		/*

		 * We might have raced with another page fault while we

		 * released the pte_offset_map_lock.

		 */

		if (!pte_same(*vmf->pte, vmf->orig_pte)) {

			pte_unmap_unlock(vmf->pte, vmf->ptl);

			return 0;

		}

		return finish_mkwrite_fault(vmf);

	}

	wp_page_reuse(vmf);

	return VM_FAULT_WRITE;
@@ -2304,7 +2327,6 @@ static int wp_page_shared(struct vm_fault *vmf) 
	__releases(vmf->ptl)

{

	struct vm_area_struct *vma = vmf->vma;

	int page_mkwrite = 0;



	get_page(vmf->page);
@@ -2318,26 +2340,17 @@ static int wp_page_shared(struct vm_fault *vmf) 
			put_page(vmf->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.

		 */

		vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd,

						vmf->address, &vmf->ptl);

		if (!pte_same(*vmf->pte, vmf->orig_pte)) {

		tmp = finish_mkwrite_fault(vmf);

		if (unlikely(!tmp || (tmp &

				      (VM_FAULT_ERROR | VM_FAULT_NOPAGE)))) {

			unlock_page(vmf->page);

			pte_unmap_unlock(vmf->pte, vmf->ptl);

			put_page(vmf->page);

			return 0;

		}

		page_mkwrite = 1;

			return tmp;

		}



	} else {

		wp_page_reuse(vmf);

	if (!page_mkwrite)

		lock_page(vmf->page);

	}

	fault_dirty_shared_page(vma, vmf->page);

	put_page(vmf->page);