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Subject: Re: [PATCH 1/1] mm: sysctl: add panic_on_inconsistent_mm sysctl
To:     Qian Cai <cai@lca.pw>, Grzegorz Halat <ghalat@redhat.com>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>, linux-fsdevel@vger.kernel.org,
        linux-doc@vger.kernel.org, ssaner@redhat.com, atomlin@redhat.com,
        oleksandr@redhat.com, vbendel@redhat.com, kirill@shutemov.name,
        khlebnikov@yandex-team.ru,
        Andrew Morton <akpm@linux-foundation.org>,
        Iurii Zaikin <yzaikin@google.com>,
        Kees Cook <keescook@chromium.org>,
        Luis Chamberlain <mcgrof@kernel.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
References: <20200129180851.551109-1-ghalat@redhat.com>
 <84C253EB-B348-4B62-B863-F192FBA8C202@lca.pw>
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Date:   Mon, 3 Feb 2020 15:08:30 +0100
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On 29.01.20 19:39, Qian Cai wrote:
> 
> 
>> On Jan 29, 2020, at 1:08 PM, Grzegorz Halat <ghalat@redhat.com> wrote:
>>
>> Memory management subsystem performs various checks at runtime,
>> if an inconsistency is detected then such event is being logged and kernel
>> continues to run. While debugging such problems it is helpful to collect
>> memory dump as early as possible. Currently, there is no easy way to panic
>> kernel when such error is detected.
>>
>> It was proposed[1] to panic the kernel if panic_on_oops is set but this
>> approach was not accepted. One of alternative proposals was introduction of
>> a new sysctl.
>>
>> Add a new sysctl - panic_on_inconsistent_mm. If the sysctl is set then the
>> kernel will be crashed when an inconsistency is detected by memory
>> management. This currently means panic when bad page or bad PTE
>> is detected(this may be extended to other places in MM).
>>
>> Another use case of this sysctl may be in security-wise environments,
>> it may be more desired to crash machine than continue to run with
>> potentially damaged data structures.
> 
> It is annoying that I have to repeat my feedback, but I don’t know why
> admins want to enable this by allowing normal users to crash the systems
> more easily through recoverable MM bugs where I am sure we have plenty.
> How does that improve the security?

There are cases where data corruption is a no-go, while "one node going down" 
is acceptable.
And then there is also the case for payed service providers that often need
a dump at the time of the problem to understand rare issues.

So I DO see value in such a thing. We should just piggy-back on panic_on_warn
I guess.