6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Peter Xu <peterx@xxxxxxxxxx> commit 8bb592c2eca8fd2bc06db7d80b38da18da4a2f43 upstream. 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@xxxxxxxxxx Fixes: df4e817b7108 ("mm: page table check") Signed-off-by: Peter Xu <peterx@xxxxxxxxxx> Reviewed-by: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx> Reviewed-by: Dan Williams <dan.j.williams@xxxxxxxxx> Reviewed-by: Alistair Popple <apopple@xxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- mm/page_table_check.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) --- a/mm/page_table_check.c +++ b/mm/page_table_check.c @@ -71,6 +71,9 @@ 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); @@ -108,6 +111,9 @@ 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); @@ -138,7 +144,10 @@ 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);
