linux-kernel - [PATCH 3/3] doc/vm: add information about page_table

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Date:   Sun, 11 Sep 2022 09:59:23 +0000
From:   Pasha Tatashin <pasha.tatashin@...een.com>
To:     pasha.tatashin@...een.com, akpm@...ux-foundation.org,
        corbet@....net, linux-mm@...ck.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, rick.p.edgecombe@...el.com
Subject: [PATCH 3/3] doc/vm: add information about page_table_check=panic

The default behavior of page table check was changed from panicking
kernel to printing a warning.

Add a note how to still panic the kernel when error is detected.

Signed-off-by: Pasha Tatashin <pasha.tatashin@...een.com>
---
 Documentation/mm/page_table_check.rst | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/Documentation/mm/page_table_check.rst b/Documentation/mm/page_table_check.rst
index 1a09472f10a3..9306cd75647c 100644
--- a/Documentation/mm/page_table_check.rst
+++ b/Documentation/mm/page_table_check.rst
@@ -16,13 +16,13 @@ Page table check performs extra verifications at the time when new pages become
 accessible from the userspace by getting their page table entries (PTEs PMDs
 etc.) added into the table.
 
-In case of detected corruption, the kernel is crashed. There is a small
-performance and memory overhead associated with the page table check. Therefore,
-it is disabled by default, but can be optionally enabled on systems where the
-extra hardening outweighs the performance costs. Also, because page table check
-is synchronous, it can help with debugging double map memory corruption issues,
-by crashing kernel at the time wrong mapping occurs instead of later which is
-often the case with memory corruptions bugs.
+In case of detected corruption, a warning is printed or kernel is crashed. There
+is a small performance and memory overhead associated with the page table check.
+Therefore, it is disabled by default, but can be optionally enabled on systems
+where the extra hardening outweighs the performance costs. Also, because page
+table check is synchronous, it can help with debugging double map memory
+corruption issues, by crashing kernel at the time wrong mapping occurs instead
+of later which is often the case with memory corruptions bugs.
 
 Double mapping detection logic
 ==============================
@@ -52,5 +52,7 @@ Build kernel with:
 
 - Boot with 'page_table_check=on' kernel parameter.
 
+- Boot with 'page_table_check=panic' in order to panic when error is detected.
+
 Optionally, build kernel with PAGE_TABLE_CHECK_ENFORCED in order to have page
 table support without extra kernel parameter.
-- 
2.37.2.789.g6183377224-goog