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mm/page_table_check: fix crash on ZONE_DEVICE

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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: df4e817b71 ("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>
This commit is contained in:
Peter Xu 2024-06-05 17:21:46 -04:00 committed by Andrew Morton
parent 8e5bd4eadd
commit 8bb592c2ec
1 changed files with 10 additions and 1 deletions
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11
mm/page_table_check.c
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@ -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);