+++ /dev/null
-From 19be0eaffa3ac7d8eb6784ad9bdbc7d67ed8e619 Mon Sep 17 00:00:00 2001
-From: Linus Torvalds <torvalds@linux-foundation.org>
-Date: Thu, 13 Oct 2016 13:07:36 -0700
-Subject: mm: remove gup_flags FOLL_WRITE games from __get_user_pages()
-
-This is an ancient bug that was actually attempted to be fixed once
-(badly) by me eleven years ago in commit 4ceb5db9757a ("Fix
-get_user_pages() race for write access") but that was then undone due to
-problems on s390 by commit f33ea7f404e5 ("fix get_user_pages bug").
-
-In the meantime, the s390 situation has long been fixed, and we can now
-fix it by checking the pte_dirty() bit properly (and do it better). The
-s390 dirty bit was implemented in abf09bed3cce ("s390/mm: implement
-software dirty bits") which made it into v3.9. Earlier kernels will
-have to look at the page state itself.
-
-Also, the VM has become more scalable, and what used a purely
-theoretical race back then has become easier to trigger.
-
-To fix it, we introduce a new internal FOLL_COW flag to mark the "yes,
-we already did a COW" rather than play racy games with FOLL_WRITE that
-is very fundamental, and then use the pte dirty flag to validate that
-the FOLL_COW flag is still valid.
-
-Reported-and-tested-by: Phil "not Paul" Oester <kernel@linuxace.com>
-Acked-by: Hugh Dickins <hughd@google.com>
-Reviewed-by: Michal Hocko <mhocko@suse.com>
-Cc: Andy Lutomirski <luto@kernel.org>
-Cc: Kees Cook <keescook@chromium.org>
-Cc: Oleg Nesterov <oleg@redhat.com>
-Cc: Willy Tarreau <w@1wt.eu>
-Cc: Nick Piggin <npiggin@gmail.com>
-Cc: Greg Thelen <gthelen@google.com>
-Cc: stable@vger.kernel.org
-Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
----
- include/linux/mm.h | 1 +
- mm/memory.c | 15 +++++++++++++-
- 2 files changed, 14 insertions(+), 2 deletions(-)
-
-diff --git a/include/linux/mm.h b/include/linux/mm.h
-index e9caec6..ed85879 100644
---- a/include/linux/mm.h
-+++ b/include/linux/mm.h
-@@ -1466,6 +1466,7 @@ static inline struct page *follow_page(struct vm_area_struct *vma,
- #define FOLL_HWPOISON 0x100 /* check page is hwpoisoned */
- #define FOLL_NUMA 0x200 /* force NUMA hinting page fault */
- #define FOLL_MIGRATION 0x400 /* wait for page to replace migration entry */
-+#define FOLL_COW 0x4000 /* internal GUP flag */
-
- typedef int (*pte_fn_t)(pte_t *pte, pgtable_t token, unsigned long addr,
- void *data);
-diff --git a/mm/memory.c b/mm/memory.c
-index b6e3037..2d8080c 100644
---- a/mm/memory.c
-+++ b/mm/memory.c
-@@ -1296,6 +1296,17 @@ int zap_vma_ptes(struct vm_area_struct *vma, unsigned long address,
- }
- EXPORT_SYMBOL_GPL(zap_vma_ptes);
-
-+/*
-+ * FOLL_FORCE can write to even unwritable pte's, but only
-+ * after we've gone through a COW cycle and they are dirty.
-+ */
-+static inline bool can_follow_write_pte(pte_t pte, unsigned int flags)
-+{
-+ return pte_write(pte) ||
-+ ((flags & FOLL_FORCE) && (flags & FOLL_COW) && pte_dirty(pte));
-+}
-+
-+
- /*
- * Do a quick page-table lookup for a single page.
- */
-@@ -1385,7 +1396,7 @@ split_fallthrough:
- migration_entry_wait(mm, pmd, address);
- goto split_fallthrough;
- }
-- if ((flags & FOLL_WRITE) && !pte_write(pte))
-+ if ((flags & FOLL_WRITE) && !can_follow_write_pte(pte, flags))
- goto unlock;
-
- page = vm_normal_page(vma, address, pte);
-@@ -1618,7 +1629,7 @@ int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
- */
- if ((ret & VM_FAULT_WRITE) &&
- !(vma->vm_flags & VM_WRITE))
-- foll_flags &= ~FOLL_WRITE;
-+ foll_flags |= FOLL_COW;
-
- cond_resched();
- }
projects / pve-kernel-2.6.32.git / blobdiff