The patch titled Subject: mm/page_table_check: fix crash on ZONE_DEVICE has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-page_table_check-fix-crash-on-zone_device.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

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: Peter Xu peterx@redhat.com Subject: mm/page_table_check: fix crash on ZONE_DEVICE Date: Wed, 5 Jun 2024 17:21:46 -0400

Not all pages may apply to pgtable check. One example is ZONE_DEVICE pages: they map PFNs directly, and they don't allocate page_ext at all even if there's struct page around. One may reference devm_memremap_pages().

When both ZONE_DEVICE and page-table-check enabled, then try to map some dax memories, one can trigger kernel bug constantly now when the kernel was trying to inject some pfn maps on the dax device:

kernel BUG at mm/page_table_check.c:55!

While it's pretty legal to use set_pxx_at() for ZONE_DEVICE pages for page fault resolutions, skip all the checks if page_ext doesn't even exist in pgtable checker, which applies to ZONE_DEVICE but maybe more.

Link: https://lkml.kernel.org/r/20240605212146.994486-1-peterx@redhat.com Signed-off-by: Peter Xu peterx@redhat.com Cc: Dan Williams dan.j.williams@intel.com Cc: Pasha Tatashin pasha.tatashin@soleen.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/page_table_check.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-)

--- a/mm/page_table_check.c~mm-page_table_check-fix-crash-on-zone_device +++ a/mm/page_table_check.c @@ -73,6 +73,9 @@ static void page_table_check_clear(unsig page = pfn_to_page(pfn); page_ext = page_ext_get(page);

+ if (!page_ext) + return; + BUG_ON(PageSlab(page)); anon = PageAnon(page);

@@ -110,6 +113,9 @@ static void page_table_check_set(unsigne page = pfn_to_page(pfn); page_ext = page_ext_get(page);

+ if (!page_ext) + return; + BUG_ON(PageSlab(page)); anon = PageAnon(page);

@@ -140,7 +146,10 @@ void __page_table_check_zero(struct page BUG_ON(PageSlab(page));

page_ext = page_ext_get(page); - BUG_ON(!page_ext); + + if (!page_ext) + return; + for (i = 0; i < (1ul << order); i++) { struct page_table_check *ptc = get_page_table_check(page_ext);

_

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

mm-page_table_check-fix-crash-on-zone_device.patch mm-debug_vm_pgtable-drop-random_orvalue-trick.patch mm-drop-leftover-comment-references-to-pxx_huge.patch