Re: [PATCH v4 1/2] mm/uffd: UFFD_FEATURE_WP_UNPOPULATED

[Peter Xu <peterx@redhat.com>]

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On Thu, Mar 09, 2023 at 05:37:10PM -0500, Peter Xu wrote:
> This is a new feature that controls how uffd-wp handles none ptes.  When
> it's set, the kernel will handle anonymous memory the same way as file
> memory, by allowing the user to wr-protect unpopulated ptes.

[...]

Hi, Andrew,

Could you add a fixup to this patch as attached?  It contains two comment
changes suggested by David, and also a oneliner fix to khugepaged (to bail
out anon thp collapsing when seeing pte markers).  The latter one was
something I spot only later on.

Thanks,

-- 
Peter Xu

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From 085596bc8913349cbeb3ec3303815f71f1a34d89 Mon Sep 17 00:00:00 2001
From: Peter Xu <peterx@redhat.com>
Date: Tue, 21 Mar 2023 16:09:26 -0400
Subject: [PATCH] fixup! mm/uffd: UFFD_FEATURE_WP_UNPOPULATED

Signed-off-by: Peter Xu <peterx@redhat.com>
---
 Documentation/admin-guide/mm/userfaultfd.rst | 2 +-
 mm/khugepaged.c                              | 2 +-
 mm/mprotect.c                                | 4 ++--
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/Documentation/admin-guide/mm/userfaultfd.rst b/Documentation/admin-guide/mm/userfaultfd.rst
index 16843d5a4f65..7c304e432205 100644
--- a/Documentation/admin-guide/mm/userfaultfd.rst
+++ b/Documentation/admin-guide/mm/userfaultfd.rst
@@ -226,7 +226,7 @@ For anonymous memory, ``ioctl(UFFDIO_WRITEPROTECT)`` will ignore none ptes
 (e.g. when pages are missing and not populated).  For file-backed memories
 like shmem and hugetlbfs, none ptes will be write protected just like a
 present pte.  In other words, there will be a userfaultfd write fault
-message generated when writting to a missing page on file typed memories,
+message generated when writing to a missing page on file typed memories,
 as long as the page range was write-protected before.  Such a message will
 not be generated on anonymous memories by default.
 
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index bdde0a02811b..2a5372c49b82 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1283,7 +1283,7 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm,
 				 * enabled swap entries.  Please see
 				 * comment below for pte_uffd_wp().
 				 */
-				if (pte_swp_uffd_wp(pteval)) {
+				if (pte_swp_uffd_wp_any(pteval)) {
 					result = SCAN_PTE_UFFD_WP;
 					goto out_unmap;
 				}
diff --git a/mm/mprotect.c b/mm/mprotect.c
index e27bbd0fde6f..b9da9a5f87fe 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -329,8 +329,8 @@ static inline int pmd_none_or_clear_bad_unless_trans_huge(pmd_t *pmd)
 }
 
 /*
- * Return true if we want to split huge thps in change protection
- * procedure, false otherwise.
+ * Return true if we want to split THPs into PTE mappings in change
+ * protection procedure, false otherwise.
  */
 static inline bool
 pgtable_split_needed(struct vm_area_struct *vma, unsigned long cp_flags)
-- 
2.39.1