mm/debug_vm_pgtable: remove pte entry from the page table

Patch series "page table check fixes and cleanups", v5.

This patch (of 4):

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:

  debug_vm_pgtable: [debug_vm_pgtable         ]: Validating architecture page table helpers
  ------------[ cut here ]------------
  kernel BUG at mm/page_table_check.c:162!
  invalid opcode: 0000 [#1] PREEMPT SMP PTI
  CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.16.0-11413-g2c271fe77d52 #3
  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.

Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Fixes: a5c3b9f ("mm/debug_vm_pgtable: add tests validating advanced arch page table helpers")
Signed-off-by: Pasha Tatashin <[email protected]>
Reviewed-by: Zi Yan <[email protected]>
Tested-by: Zi Yan <[email protected]>
Acked-by: David Rientjes <[email protected]>
Reviewed-by: Anshuman Khandual <[email protected]>
Cc: Paul Turner <[email protected]>
Cc: Wei Xu <[email protected]>
Cc: Greg Thelen <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Mike Rapoport <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Aneesh Kumar K.V <[email protected]>
Cc: Jiri Slaby <[email protected]>
Cc: Muchun Song <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: <[email protected]>	[5.9+]
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: soleen

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)