Commit 8bb592c2 authored Jun 05, 2024 by Peter Xu Committed by Andrew Morton Jun 15, 2024

mm/page_table_check: fix crash on ZONE_DEVICE

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


Fixes: df4e817b ("mm: page table check")
Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Alistair Popple <apopple@nvidia.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

parent 8e5bd4ea

mm/page_table_check.c

+10 −1

Original line number	Diff line number	Diff line
		@@ -73,6 +73,9 @@ static void page_table_check_clear(unsigned long pfn, unsigned long pgcnt)
		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(unsigned long pfn, unsigned long pgcnt,
		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 *page, unsigned int order)
		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);