The quilt patch titled
Subject: pgtable: improve pte_protnone() comment
has been removed from the -mm tree. Its filename was
pgtable-improve-pte_protnone-comment.patch
This patch was dropped because it was merged into the mm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
------------------------------------------------------
From: David Hildenbrand <david@xxxxxxxxxx>
Subject: pgtable: improve pte_protnone() comment
Date: Thu, 3 Aug 2023 16:32:06 +0200
Especially the "For PROT_NONE VMAs, the PTEs are not marked
_PAGE_PROTNONE" part is wrong: doing an mprotect(PROT_NONE) will end up
marking all PTEs on x86_64 as _PAGE_PROTNONE, making pte_protnone()
indicate "yes".
So let's improve the comment, so it's easier to grasp which semantics
pte_protnone() actually has.
Link: https://lkml.kernel.org/r/20230803143208.383663-6-david@xxxxxxxxxx
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Acked-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: liubo <liubo254@xxxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Shuah Khan <shuah@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/pgtable.h | 16 ++++++++++------
1 file changed, 10 insertions(+), 6 deletions(-)
--- a/include/linux/pgtable.h~pgtable-improve-pte_protnone-comment
+++ a/include/linux/pgtable.h
@@ -1333,12 +1333,16 @@ static inline int pud_trans_unstable(pud
#ifndef CONFIG_NUMA_BALANCING
/*
- * Technically a PTE can be PROTNONE even when not doing NUMA balancing but
- * the only case the kernel cares is for NUMA balancing and is only ever set
- * when the VMA is accessible. For PROT_NONE VMAs, the PTEs are not marked
- * _PAGE_PROTNONE so by default, implement the helper as "always no". It
- * is the responsibility of the caller to distinguish between PROT_NONE
- * protections and NUMA hinting fault protections.
+ * In an inaccessible (PROT_NONE) VMA, pte_protnone() may indicate "yes". It is
+ * perfectly valid to indicate "no" in that case, which is why our default
+ * implementation defaults to "always no".
+ *
+ * In an accessible VMA, however, pte_protnone() reliably indicates PROT_NONE
+ * page protection due to NUMA hinting. NUMA hinting faults only apply in
+ * accessible VMAs.
+ *
+ * So, to reliably identify PROT_NONE PTEs that require a NUMA hinting fault,
+ * looking at the VMA accessibility is sufficient.
*/
static inline int pte_protnone(pte_t pte)
{
_
Patches currently in -mm which might be from david@xxxxxxxxxx are
mm-swap-stop-using-page-private-on-tail-pages-for-thp_swap.patch
mm-swap-inline-folio_set_swap_entry-and-folio_swap_entry.patch
mm-huge_memory-work-on-folio-swap-instead-of-page-private-when-splitting-folio.patch
