+ mm-hugetlb-proc-check-for-hugetlb-shared-pmd-in-proc-pid-smaps.patch added to mm-hotfixes-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm: hugetlb: proc: check for hugetlb shared PMD in /proc/PID/smaps
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mm-hugetlb-proc-check-for-hugetlb-shared-pmd-in-proc-pid-smaps.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-hugetlb-proc-check-for-hugetlb-shared-pmd-in-proc-pid-smaps.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: Mike Kravetz <mike.kravetz@oracle.com>
Subject: mm: hugetlb: proc: check for hugetlb shared PMD in /proc/PID/smaps
Date: Thu, 26 Jan 2023 14:27:20 -0800

Patch series "Fixes for hugetlb mapcount at most 1 for shared PMDs".

This issue of mapcount in hugetlb pages referenced by shared PMDs was
discussed in [1].  The following two patches address user visible behavior
caused by this issue.

[1] https://lore.kernel.org/linux-mm/Y9BF+OCdWnCSilEu@monkey/


This patch (of 2):

A hugetlb page will have a mapcount of 1 if mapped by multiple processes
via a shared PMD.  This is because only the first process increases the
map count, and subsequent processes just add the shared PMD page to their
page table.

page_mapcount is being used to decide if a hugetlb page is shared or
private in /proc/PID/smaps.  Pages referenced via a shared PMD were
incorrectly being counted as private.

To fix, check for a shared PMD if mapcount is 1.  If a shared PMD is found
count the hugetlb page as shared.  A new helper to check for a shared PMD
is added.

Link: https://lkml.kernel.org/r/20230126222721.222195-2-mike.kravetz@oracle.com
Fixes: 25ee01a2fca0 ("mm: hugetlb: proc: add hugetlb-related fields to /proc/PID/smaps")
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: James Houghton <jthoughton@google.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Naoya Horiguchi <naoya.horiguchi@linux.dev>
Cc: Peter Xu <peterx@redhat.com>
Cc: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/proc/task_mmu.c      |   10 ++++++++--
 include/linux/hugetlb.h |   12 ++++++++++++
 2 files changed, 20 insertions(+), 2 deletions(-)

--- a/fs/proc/task_mmu.c~mm-hugetlb-proc-check-for-hugetlb-shared-pmd-in-proc-pid-smaps
+++ a/fs/proc/task_mmu.c
@@ -749,8 +749,14 @@ static int smaps_hugetlb_range(pte_t *pt
 
 		if (mapcount >= 2)
 			mss->shared_hugetlb += huge_page_size(hstate_vma(vma));
-		else
-			mss->private_hugetlb += huge_page_size(hstate_vma(vma));
+		else {
+			if (hugetlb_pmd_shared(pte))
+				mss->shared_hugetlb +=
+						huge_page_size(hstate_vma(vma));
+			else
+				mss->private_hugetlb +=
+						huge_page_size(hstate_vma(vma));
+		}
 	}
 	return 0;
 }
--- a/include/linux/hugetlb.h~mm-hugetlb-proc-check-for-hugetlb-shared-pmd-in-proc-pid-smaps
+++ a/include/linux/hugetlb.h
@@ -1187,6 +1187,18 @@ static inline __init void hugetlb_cma_re
 }
 #endif
 
+#ifdef CONFIG_ARCH_WANT_HUGE_PMD_SHARE
+static inline bool hugetlb_pmd_shared(pte_t *pte)
+{
+	return page_count(virt_to_page(pte)) > 1;
+}
+#else
+static inline bool hugetlb_pmd_shared(pte_t *pte)
+{
+	return false;
+}
+#endif
+
 bool want_pmd_share(struct vm_area_struct *vma, unsigned long addr);
 
 #ifndef __HAVE_ARCH_FLUSH_HUGETLB_TLB_RANGE
_

Patches currently in -mm which might be from mike.kravetz@oracle.com are

mm-hugetlb-proc-check-for-hugetlb-shared-pmd-in-proc-pid-smaps.patch
migrate-hugetlb-check-for-hugetlb-shared-pmd-in-node-migration.patch