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authorLinus Torvalds <torvalds@linux-foundation.org>2020-09-04 09:31:54 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2020-09-04 09:31:54 -0700
commitb25d1dc9474e1f0cefca994885e82beea271acfe (patch)
tree27b4216414a6ccb5cc65999a0c249d005f01d1cf /mm/memory.c
parentcfc905f158eaa099d6258031614d11869e7ef71c (diff)
parent798a6b87ecd72828a6c6b5469aaa2032a57e92b7 (diff)
Merge branch 'simplify-do_wp_page'
Merge emailed patches from Peter Xu: "This is a small series that I picked up from Linus's suggestion to simplify cow handling (and also make it more strict) by checking against page refcounts rather than mapcounts. This makes uffd-wp work again (verified by running upmapsort)" Note: this is horrendously bad timing, and making this kind of fundamental vm change after -rc3 is not at all how things should work. The saving grace is that it really is a a nice simplification: 8 files changed, 29 insertions(+), 120 deletions(-) The reason for the bad timing is that it turns out that commit 17839856fd58 ("gup: document and work around 'COW can break either way' issue" broke not just UFFD functionality (as Peter noticed), but Mikulas Patocka also reports that it caused issues for strace when running in a DAX environment with ext4 on a persistent memory setup. And we can't just revert that commit without re-introducing the original issue that is a potential security hole, so making COW stricter (and in the process much simpler) is a step to then undoing the forced COW that broke other uses. Link: https://lore.kernel.org/lkml/alpine.LRH.2.02.2009031328040.6929@file01.intranet.prod.int.rdu2.redhat.com/ * emailed patches from Peter Xu <peterx@redhat.com>: mm: Add PGREUSE counter mm/gup: Remove enfornced COW mechanism mm/ksm: Remove reuse_ksm_page() mm: do_wp_page() simplification
Diffstat (limited to 'mm/memory.c')
-rw-r--r--mm/memory.c60
1 files changed, 18 insertions, 42 deletions
diff --git a/mm/memory.c b/mm/memory.c
index 602f4283122f..148eafb8cbb1 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2622,6 +2622,7 @@ static inline void wp_page_reuse(struct vm_fault *vmf)
if (ptep_set_access_flags(vma, vmf->address, vmf->pte, entry, 1))
update_mmu_cache(vma, vmf->address, vmf->pte);
pte_unmap_unlock(vmf->pte, vmf->ptl);
+ count_vm_event(PGREUSE);
}
/*
@@ -2927,50 +2928,25 @@ static vm_fault_t do_wp_page(struct vm_fault *vmf)
* not dirty accountable.
*/
if (PageAnon(vmf->page)) {
- int total_map_swapcount;
- if (PageKsm(vmf->page) && (PageSwapCache(vmf->page) ||
- page_count(vmf->page) != 1))
+ struct page *page = vmf->page;
+
+ /* PageKsm() doesn't necessarily raise the page refcount */
+ if (PageKsm(page) || page_count(page) != 1)
+ goto copy;
+ if (!trylock_page(page))
+ goto copy;
+ if (PageKsm(page) || page_mapcount(page) != 1 || page_count(page) != 1) {
+ unlock_page(page);
goto copy;
- if (!trylock_page(vmf->page)) {
- get_page(vmf->page);
- pte_unmap_unlock(vmf->pte, vmf->ptl);
- lock_page(vmf->page);
- vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd,
- vmf->address, &vmf->ptl);
- if (!pte_same(*vmf->pte, vmf->orig_pte)) {
- update_mmu_tlb(vma, vmf->address, vmf->pte);
- unlock_page(vmf->page);
- pte_unmap_unlock(vmf->pte, vmf->ptl);
- put_page(vmf->page);
- return 0;
- }
- put_page(vmf->page);
- }
- if (PageKsm(vmf->page)) {
- bool reused = reuse_ksm_page(vmf->page, vmf->vma,
- vmf->address);
- unlock_page(vmf->page);
- if (!reused)
- goto copy;
- wp_page_reuse(vmf);
- return VM_FAULT_WRITE;
- }
- if (reuse_swap_page(vmf->page, &total_map_swapcount)) {
- if (total_map_swapcount == 1) {
- /*
- * The page is all ours. Move it to
- * our anon_vma so the rmap code will
- * not search our parent or siblings.
- * Protected against the rmap code by
- * the page lock.
- */
- page_move_anon_rmap(vmf->page, vma);
- }
- unlock_page(vmf->page);
- wp_page_reuse(vmf);
- return VM_FAULT_WRITE;
}
- unlock_page(vmf->page);
+ /*
+ * Ok, we've got the only map reference, and the only
+ * page count reference, and the page is locked,
+ * it's dark out, and we're wearing sunglasses. Hit it.
+ */
+ wp_page_reuse(vmf);
+ unlock_page(page);
+ return VM_FAULT_WRITE;
} else if (unlikely((vma->vm_flags & (VM_WRITE|VM_SHARED)) ==
(VM_WRITE|VM_SHARED))) {
return wp_page_shared(vmf);