[PATCH v5 1/4] mm/debug_vm_pgtable: remove pte entry from the page table

[Pasha Tatashin <pasha.tatashin@soleen.com>]

The pte entry that is used in pte_advanced_tests() is never removed from
the page table at the end of the test.

The issue is detected by page_table_check, to repro compile kernel with
the following configs:

CONFIG_DEBUG_VM_PGTABLE=y
CONFIG_PAGE_TABLE_CHECK=y
CONFIG_PAGE_TABLE_CHECK_ENFORCED=y

During the boot the following BUG is printed:

[    2.262821] debug_vm_pgtable: [debug_vm_pgtable         ]: Validating
               architecture page table helpers
[    2.276826] ------------[ cut here ]------------
[    2.280426] kernel BUG at mm/page_table_check.c:162!
[    2.284118] invalid opcode: 0000 [#1] PREEMPT SMP PTI
[    2.287787] CPU: 0 PID: 1 Comm: swapper/0 Not tainted
               5.16.0-11413-g2c271fe77d52 #3
[    2.293226] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
               BIOS rel-1.15.0-0-g2dd4b9b3f840-prebuilt.qemu.org
               04/01/2014
...

The entry should be properly removed from the page table before the page
is released to the free list.

Fixes: a5c3b9ffb0f4 ("mm/debug_vm_pgtable: add tests validating advanced arch page table helpers")
Cc: stable@vger.kernel.org # 5.9+

Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Tested-by: Zi Yan <ziy@nvidia.com>
Acked-by: David Rientjes <rientjes@google.com>
---
 mm/debug_vm_pgtable.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
index a7ac97c76762..db2abd9e415b 100644
--- a/mm/debug_vm_pgtable.c
+++ b/mm/debug_vm_pgtable.c
@@ -171,6 +171,8 @@ static void __init pte_advanced_tests(struct pgtable_debug_args *args)
 	ptep_test_and_clear_young(args->vma, args->vaddr, args->ptep);
 	pte = ptep_get(args->ptep);
 	WARN_ON(pte_young(pte));
+
+	ptep_get_and_clear_full(args->mm, args->vaddr, args->ptep, 1);
 }
 
 static void __init pte_savedwrite_tests(struct pgtable_debug_args *args)
-- 
2.35.0.rc2.247.g8bbb082509-goog