linux-kernel - Re: [PATCH v2 2/3] doc/vm: add information about page_table_check warn

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Date:   Sat, 22 Jul 2023 16:59:15 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Pasha Tatashin <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: Re: [PATCH v2 2/3] doc/vm: add information about page_table_check
 warn_on behavior

Hi--

On 7/22/23 16:15, Pasha Tatashin wrote:
> 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 | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/mm/page_table_check.rst b/Documentation/mm/page_table_check.rst
> index c12838ce6b8d..f534c80ee9c9 100644
> --- a/Documentation/mm/page_table_check.rst
> +++ b/Documentation/mm/page_table_check.rst
> @@ -14,13 +14,14 @@ 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
> +In case of detected corruption, a warning is printed. 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.
> +often the case with memory corruptions bugs. In order to crash kernel sysctl
> +panic_on_warn should be set to 1.

Better as:
   In order to crash the kernel, the sysctl panic_on_warn should be set 
to 1.