linux-kernel - [PATCH 1/3] mm/debug_vm_pgtable: remove pte entry from the page table

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Date:   Thu, 20 Jan 2022 04:25:11 +0000
From:   Pasha Tatashin <pasha.tatashin@...een.com>
To:     pasha.tatashin@...een.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, akpm@...ux-foundation.org, rientjes@...gle.com,
        pjt@...gle.com, weixugc@...gle.com, gthelen@...gle.com,
        mingo@...hat.com, will@...nel.org, rppt@...nel.org,
        dave.hansen@...ux.intel.com, hpa@...or.com,
        aneesh.kumar@...ux.ibm.com, jirislaby@...nel.org,
        songmuchun@...edance.com, qydwhotmail@...il.com, hughd@...gle.com,
        ziy@...dia.com, anshuman.khandual@....com
Subject: [PATCH 1/3] mm/debug_vm_pgtable: remove pte entry from the page table

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:

[    7.483050][    T1] debug_vm_pgtable: [debug_vm_pgtable         ]:
Validating architecture page tabs
[    7.490930][    T1] ------------[ cut here ]------------
[    7.494926][    T1] kernel BUG at mm/page_table_check.c:194!
[    7.499172][    T1] invalid opcode: 0000 [#1] PREEMPT SMP KASAN
[    7.503610][    T1] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.16.0+
[    7.508600][    T1] Hardware name: QEMU Standard PC (i440FX + PIIX,
...

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")

Signed-off-by: Pasha Tatashin <pasha.tatashin@...een.com>
---
 mm/debug_vm_pgtable.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
index a7ac97c76762..f7c5970f1719 100644
--- a/mm/debug_vm_pgtable.c
+++ b/mm/debug_vm_pgtable.c
@@ -171,6 +171,7 @@ 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)
-- 
2.34.1.703.g22d0c6ccf7-goog