The patch below does not apply to the 6.1-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
To reproduce the conflict and resubmit, you may use the following commands:
git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y git checkout FETCH_HEAD git cherry-pick -x 1013af4f585fccc4d3e5c5824d174de2257f7d6d # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2025062054-snowdrop-stitch-3abf@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^..
Possible dependencies:
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 1013af4f585fccc4d3e5c5824d174de2257f7d6d Mon Sep 17 00:00:00 2001 From: Jann Horn jannh@google.com Date: Tue, 27 May 2025 23:23:54 +0200 Subject: [PATCH] mm/hugetlb: fix huge_pmd_unshare() vs GUP-fast race
huge_pmd_unshare() drops a reference on a page table that may have previously been shared across processes, potentially turning it into a normal page table used in another process in which unrelated VMAs can afterwards be installed.
If this happens in the middle of a concurrent gup_fast(), gup_fast() could end up walking the page tables of another process. While I don't see any way in which that immediately leads to kernel memory corruption, it is really weird and unexpected.
Fix it with an explicit broadcast IPI through tlb_remove_table_sync_one(), just like we do in khugepaged when removing page tables for a THP collapse.
Link: https://lkml.kernel.org/r/20250528-hugetlb-fixes-splitrace-v2-2-1329349bad1a... Link: https://lkml.kernel.org/r/20250527-hugetlb-fixes-splitrace-v1-2-f4136f5ec58a... Fixes: 39dde65c9940 ("[PATCH] shared page table for hugetlb page") Signed-off-by: Jann Horn jannh@google.com Reviewed-by: Lorenzo Stoakes lorenzo.stoakes@oracle.com Cc: Liam Howlett liam.howlett@oracle.com Cc: Muchun Song muchun.song@linux.dev Cc: Oscar Salvador osalvador@suse.de Cc: Vlastimil Babka vbabka@suse.cz Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org
diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 7ba020d489d4..8746ed2fec13 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -7629,6 +7629,13 @@ int huge_pmd_unshare(struct mm_struct *mm, struct vm_area_struct *vma, return 0;
pud_clear(pud); + /* + * Once our caller drops the rmap lock, some other process might be + * using this page table as a normal, non-hugetlb page table. + * Wait for pending gup_fast() in other threads to finish before letting + * that happen. + */ + tlb_remove_table_sync_one(); ptdesc_pmd_pts_dec(virt_to_ptdesc(ptep)); mm_dec_nr_pmds(mm); return 1;