> >> Can we assume mmu_notifier is only used by kvm now?
> >> if not, we need to make new notifier.
> >
> > KVM is no fundamentally different from other users in this respect, so
> > I don't see why need a new notifier. If it works for others it'll work
> > for KVM and the other way around is true too.
> >
> > mmu notifier users can or cannot take a page pin. KVM does. GRU
> > doesn't. XPMEM does. All of them releases any pin after
> > mmu_notifier_invalidate_page. All that is important is to run
> > mmu_notifier_invalidate_page _after_ the ptep_clear_young_notify, so
> > that we don't nuke secondary mappings on the pages unless we really go
> > to nuke the pte.
>
> Thank you kindful explain. I understand it :)
How about this?
---
mm/rmap.c | 50 +++++++++++++++++++++++++++++++++++++++++++-------
mm/swapfile.c | 3 ++-
2 files changed, 45 insertions(+), 8 deletions(-)
Index: b/mm/swapfile.c
===================================================================
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -547,7 +547,8 @@ int reuse_swap_page(struct page *page)
SetPageDirty(page);
}
}
- return count == 1;
+
+ return count + page_count(page) == 2;
}
/*
Index: b/mm/rmap.c
===================================================================
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -772,12 +772,34 @@ static int try_to_unmap_one(struct page
if (!pte)
goto out;
- /*
- * If the page is mlock()d, we cannot swap it out.
- * If it's recently referenced (perhaps page_referenced
- * skipped over this mm) then we should reactivate it.
- */
+
+ /* Unpinning the page from long time pinning subsystem (e.g. kvm). */
+ mmu_notifier_invalidate_page(vma->vm_mm, address);
+
if (!migration) {
+ /*
+ * Don't pull an anonymous page out from under get_user_pages.
+ * get_user_pages_fast() silently raises page count without any
+ * lock. thus, we need twice check here and _after_ pte nuking.
+ *
+ * If nuke the pte of pinned pages, do_wp_page() will replace
+ * it by a copy page, and the user never get to see the data
+ * GUP was holding the original page for.
+ *
+ * note:
+ * page_mapcount() + 2 mean pte + swapcache + us
+ */
+ if (PageAnon(page) &&
+ (page_count(page) != page_mapcount(page) + 2)) {
+ ret = SWAP_FAIL;
+ goto out_unmap;
+ }
+
+ /*
+ * If the page is mlock()d, we cannot swap it out.
+ * If it's recently referenced (perhaps page_referenced
+ * skipped over this mm) then we should reactivate it.
+ */
if (vma->vm_flags & VM_LOCKED) {
ret = SWAP_MLOCK;
goto out_unmap;
@@ -786,11 +808,25 @@ static int try_to_unmap_one(struct page
ret = SWAP_FAIL;
goto out_unmap;
}
- }
+ }
/* Nuke the page table entry. */
flush_cache_page(vma, address, page_to_pfn(page));
- pteval = ptep_clear_flush_notify(vma, address, pte);
+ pteval = ptep_clear_flush(vma, address, pte);
+
+ if (!migration) {
+ if (PageAnon(page) &&
+ page_count(page) != page_mapcount(page) + 2) {
+ /*
+ * We lose the race against get_user_pages_fast().
+ * set the same pte and give up unmapping.
+ */
+ set_pte_at(mm, address, pte, pteval);
+ ret = SWAP_FAIL;
+ goto out_unmap;
+ }
+ }
+
/* Move the dirty bit to the physical page now the pte is gone. */
if (pte_dirty(pteval))
--
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