+ mm-gup-fix-follow_devmap_pd-on-page==null-handling.patch added to mm-unstable branch

+ mm-gup-fix-follow_devmap_pd-on-page==null-handling.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm/gup: fix follow_devmap_p[mu]d() on page==NULL handling
has been added to the -mm mm-unstable branch.  Its filename is
     mm-gup-fix-follow_devmap_pd-on-page==null-handling.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-gup-fix-follow_devmap_pd-on-page==null-handling.patch

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

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------------------------------------------------------
From: Peter Xu <peterx@redhat.com>
Subject: mm/gup: fix follow_devmap_p[mu]d() on page==NULL handling
Date: Thu, 23 Nov 2023 13:02:22 -0500

This is a bug found not by any report but only by code observations.

When GUP sees a devpmd/devpud and if page==NULL is returned, it means a
fault is probably required.  Here falling through when page==NULL can
cause unexpected behavior.

Fix both cases by catching the page==NULL cases with no_page_table().

Link: https://lkml.kernel.org/r/20231123180222.1048297-1-peterx@redhat.com
Fixes: 3565fce3a659 ("mm, x86: get_user_pages() for dax mappings")
Fixes: 080dbb618b4b ("mm/follow_page_mask: split follow_page_mask to smaller functions.")
Signed-off-by: Peter Xu <peterx@redhat.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/gup.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/mm/gup.c~mm-gup-fix-follow_devmap_pd-on-page==null-handling
+++ a/mm/gup.c
@@ -710,6 +710,7 @@ static struct page *follow_pmd_mask(stru
 		spin_unlock(ptl);
 		if (page)
 			return page;
+		return no_page_table(vma, flags);
 	}
 	if (likely(!pmd_trans_huge(pmdval)))
 		return follow_page_pte(vma, address, pmd, flags, &ctx->pgmap);
@@ -758,6 +759,7 @@ static struct page *follow_pud_mask(stru
 		spin_unlock(ptl);
 		if (page)
 			return page;
+		return no_page_table(vma, flags);
 	}
 	if (unlikely(pud_bad(*pud)))
 		return no_page_table(vma, flags);
_

Patches currently in -mm which might be from peterx@redhat.com are

mm-pagemap-fix-ioctlpagemap_scan-on-vma-check.patch
mm-pagemap-fix-wr-protect-even-if-pm_scan_wp_matching-not-set.patch
mm-selftests-fix-pagemap_ioctl-memory-map-test.patch
mm-kconfig-make-userfaultfd-a-menuconfig.patch
fs-kconfig-make-hugetlbfs-a-menuconfig.patch
mm-gup-fix-follow_devmap_pd-on-page==null-handling.patch