This is a note to let you know that I've just added the patch titled
hugetlb: fix huge_pmd_unshare address update
to the 5.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
hugetlb-fix-huge_pmd_unshare-address-update.patch
and it can be found in the queue-5.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 48381273f8734d28ef56a5bdf1966dd8530111bc Mon Sep 17 00:00:00 2001
From: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Date: Tue, 24 May 2022 13:50:03 -0700
Subject: hugetlb: fix huge_pmd_unshare address update
From: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
commit 48381273f8734d28ef56a5bdf1966dd8530111bc upstream.
The routine huge_pmd_unshare() is passed a pointer to an address
associated with an area which may be unshared. If unshare is successful
this address is updated to 'optimize' callers iterating over huge page
addresses. For the optimization to work correctly, address should be
updated to the last huge page in the unmapped/unshared area. However, in
the common case where the passed address is PUD_SIZE aligned, the address
is incorrectly updated to the address of the preceding huge page. That
wastes CPU cycles as the unmapped/unshared range is scanned twice.
Link: https://lkml.kernel.org/r/20220524205003.126184-1-mike.kravetz@xxxxxxxxxx
Fixes: 39dde65c9940 ("shared page table for hugetlb page")
Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Acked-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
mm/hugetlb.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -5033,7 +5033,14 @@ int huge_pmd_unshare(struct mm_struct *m
pud_clear(pud);
put_page(virt_to_page(ptep));
mm_dec_nr_pmds(mm);
- *addr = ALIGN(*addr, HPAGE_SIZE * PTRS_PER_PTE) - HPAGE_SIZE;
+ /*
+ * This update of passed address optimizes loops sequentially
+ * processing addresses in increments of huge page size (PMD_SIZE
+ * in this case). By clearing the pud, a PUD_SIZE area is unmapped.
+ * Update address to the 'last page' in the cleared area so that
+ * calling loop can move to first page past this area.
+ */
+ *addr |= PUD_SIZE - PMD_SIZE;
return 1;
}
#define want_pmd_share() (1)
Patches currently in stable-queue which might be from mike.kravetz@xxxxxxxxxx are
queue-5.4/hugetlb-fix-huge_pmd_unshare-address-update.patch
