linux-kernel - Re: [PATCH 2/3] mm/page_table_check: Do WARN_ON instead of BUG

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Message-ID: <CA+CK2bD5ae0oUefiGMAzxun4-rJhqUdfJqbzcCkZM_Uek-KTxQ@mail.gmail.com>
Date:   Sun, 11 Sep 2022 16:42:34 -0400
From:   Pasha Tatashin <pasha.tatashin@...een.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Jonathan Corbet <corbet@....net>,
        linux-mm <linux-mm@...ck.org>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>
Subject: Re: [PATCH 2/3] mm/page_table_check: Do WARN_ON instead of BUG_ON by default

On Sun, Sep 11, 2022 at 12:08 PM Matthew Wilcox <willy@...radead.org> wrote:
>
> On Sun, Sep 11, 2022 at 09:59:22AM +0000, Pasha Tatashin wrote:
> > Currently, page_table_check when detects errors panics kernel. Instead,
> > print a warning, and panic only when specifically requested via kernel
> > parameter:
> >
> >       page_table_check=panic
>
> Why are the page table checks so special that they deserve their own
> command line parameter?  Why shouldn't this be controlled by the usual
> panic_on_warn option?

page_table_check can be used as a security feature preventing false
page sharing between address spaces. For example, at Google we want it
to keep enabled on production systems, yet we do not want to enable
panic_on_warn as it would cause panics for many other reasons which
are security unrelated.

Pasha