The patch titled Subject: hugetlb: fix huge_pmd_unshare address update has been added to the -mm mm-hotfixes-unstable branch. Its filename is hugetlb-fix-huge_pmd_unshare-address-update.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Mike Kravetz mike.kravetz@oracle.com Subject: hugetlb: fix huge_pmd_unshare address update Date: Tue, 24 May 2022 13:50:03 -0700

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@oracle.com Fixes: 39dde65c9940 ("shared page table for hugetlb page") Signed-off-by: Mike Kravetz mike.kravetz@oracle.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/hugetlb.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-)

--- a/mm/hugetlb.c~hugetlb-fix-huge_pmd_unshare-address-update +++ a/mm/hugetlb.c @@ -6562,7 +6562,14 @@ 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; }

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

hugetlb-fix-huge_pmd_unshare-address-update.patch