Commit 920fc356 authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
Browse files

[PATCH] unpaged: COW on VM_UNPAGED 



Remove the BUG_ON(vma->vm_flags & VM_UNPAGED) from do_wp_page, and let it do
Copy-On-Write without touching the VM_UNPAGED's page counts - but this is
incomplete, because the anonymous page it inserts will itself need to be
handled, here and in other functions - next patch.

We still don't copy the page if the pfn is invalid, because the
copy_user_highpage interface does not allow it.  But that's not been a problem
in the past: can be added in later if the need arises.

Signed-off-by: default avatarHugh Dickins <hugh@veritas.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 101d2be7

mm/memory.c

+25 −12
Original line number Diff line number Diff line
@@ -1277,22 +1277,28 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma, 
		unsigned long address, pte_t *page_table, pmd_t *pmd,

		spinlock_t *ptl, pte_t orig_pte)

{

	struct page *old_page, *new_page;

	struct page *old_page, *src_page, *new_page;

	unsigned long pfn = pte_pfn(orig_pte);

	pte_t entry;

	int ret = VM_FAULT_MINOR;



	BUG_ON(vma->vm_flags & VM_UNPAGED);



	if (unlikely(!pfn_valid(pfn))) {

		/*

		 * Page table corrupted: show pte and kill process.

		 * Or it's an attempt to COW an out-of-map VM_UNPAGED

		 * entry, which copy_user_highpage does not support.

		 */

		print_bad_pte(vma, orig_pte, address);

		ret = VM_FAULT_OOM;

		goto unlock;

	}

	old_page = pfn_to_page(pfn);

	src_page = old_page;



	if (unlikely(vma->vm_flags & VM_UNPAGED)) {

		old_page = NULL;

		goto gotten;

	}



	if (PageAnon(old_page) && !TestSetPageLocked(old_page)) {

		int reuse = can_share_swap_page(old_page);
@@ -1313,11 +1319,12 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma, 
	 * Ok, we need to copy. Oh, well..

	 */

	page_cache_get(old_page);

gotten:

	pte_unmap_unlock(page_table, ptl);



	if (unlikely(anon_vma_prepare(vma)))

		goto oom;

	if (old_page == ZERO_PAGE(address)) {

	if (src_page == ZERO_PAGE(address)) {

		new_page = alloc_zeroed_user_highpage(vma, address);

		if (!new_page)

			goto oom;
@@ -1325,7 +1332,7 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma, 
		new_page = alloc_page_vma(GFP_HIGHUSER, vma, address);

		if (!new_page)

			goto oom;

		copy_user_highpage(new_page, old_page, address);

		copy_user_highpage(new_page, src_page, address);

	}



	/*
@@ -1333,11 +1340,14 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma, 
	 */

	page_table = pte_offset_map_lock(mm, pmd, address, &ptl);

	if (likely(pte_same(*page_table, orig_pte))) {

		if (old_page) {

			page_remove_rmap(old_page);

			if (!PageAnon(old_page)) {

			inc_mm_counter(mm, anon_rss);

				dec_mm_counter(mm, file_rss);

				inc_mm_counter(mm, anon_rss);

			}

		} else

			inc_mm_counter(mm, anon_rss);

		flush_cache_page(vma, address, pfn);

		entry = mk_pte(new_page, vma->vm_page_prot);

		entry = maybe_mkwrite(pte_mkdirty(entry), vma);
@@ -1351,12 +1361,15 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma, 
		new_page = old_page;

		ret |= VM_FAULT_WRITE;

	}

	if (new_page)

		page_cache_release(new_page);

	if (old_page)

		page_cache_release(old_page);

unlock:

	pte_unmap_unlock(page_table, ptl);

	return ret;

oom:

	if (old_page)

		page_cache_release(old_page);

	return VM_FAULT_OOM;

}

CRA Git | Maintained and supported by SUSTech CRA and CCSE