The patch titled
Subject: mm/memory: fix missing pte marker for !page on pte zaps
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-memory-fix-missing-pte-marker-for-page-on-pte-zaps.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-memory-fix-missing-pte-marker-for-page-on-pte-zaps.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days
------------------------------------------------------
From: Peter Xu <peterx@xxxxxxxxxx>
Subject: mm/memory: fix missing pte marker for !page on pte zaps
Date: Wed, 13 Mar 2024 17:31:07 -0400
Commit 0cf18e839f64 of large folio zap work broke uffd-wp. Now mm's uffd
unit test "wp-unpopulated" will trigger this WARN_ON_ONCE().
The WARN_ON_ONCE() asserts that an VMA cannot be registered with
userfaultfd-wp if it contains a !normal page, but it's actually possible.
One example is an anonymous vma, register with uffd-wp, read anything will
install a zero page. Then when zap on it, this should trigger.
What's more, removing that WARN_ON_ONCE may not be enough either, because
we should also not rely on "whether it's a normal page" to decide whether
pte marker is needed. For example, one can register wr-protect over some
DAX regions to track writes when UFFD_FEATURE_WP_ASYNC enabled, in which
case it can have page==NULL for a devmap but we may want to keep the
marker around.
Link: https://lkml.kernel.org/r/20240313213107.235067-1-peterx@xxxxxxxxxx
Fixes: 0cf18e839f64 ("mm/memory: handle !page case in zap_present_pte() separately")
Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Cc: Muhammad Usama Anjum <usama.anjum@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memory.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
--- a/mm/memory.c~mm-memory-fix-missing-pte-marker-for-page-on-pte-zaps
+++ a/mm/memory.c
@@ -1536,7 +1536,9 @@ static inline int zap_present_ptes(struc
ptep_get_and_clear_full(mm, addr, pte, tlb->fullmm);
arch_check_zapped_pte(vma, ptent);
tlb_remove_tlb_entry(tlb, pte, addr);
- VM_WARN_ON_ONCE(userfaultfd_wp(vma));
+ if (userfaultfd_pte_wp(vma, ptent))
+ zap_install_uffd_wp_if_needed(vma, addr, pte, 1,
+ details, ptent);
ksm_might_unmap_zero_page(mm, ptent);
return 1;
}
_
Patches currently in -mm which might be from peterx@xxxxxxxxxx are
mm-memory-fix-missing-pte-marker-for-page-on-pte-zaps.patch
