Message-ID: <a391e98c-88af-886c-0426-c41c9980afa1@redhat.com>
Date:   Tue, 24 Jan 2023 19:01:49 +0100
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To:     Stefan Roesch <shr@devkernel.io>
Cc:     linux-mm@kvack.org, linux-doc@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-kselftest@vger.kernel.org,
        linux-trace-kernel@vger.kernel.org, CGEL <cgel.zte@gmail.com>,
        Michal Hocko <mhocko@kernel.org>, Jann Horn <jannh@google.com>
References: <20230123173748.1734238-1-shr@devkernel.io>
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 <qvqwbkmnj014.fsf@dev0134.prn3.facebook.com>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
Subject: Re: [RESEND RFC PATCH v1 00/20] mm: process/cgroup ksm support
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[...]

>> I'm going to point out the security aspect, and that e.g., Windows used to
>> enable it system-wide before getting taught by security experts otherwise.
>> Details on KSM and security aspects can be found in that thread.
>>
> If I'm not mistaken the security aspect exists today. When KSM is
> enabled with madvise this is the same.

Yes, and we mostly only use it for virtual machines -- and to be 
precise, guest memory only -- where it has to be enabled explicitly on a 
well documented basis ...

Impossible for an admin to force it on other parts of the hypervisor 
process that might be more security sensitive. Or on other arbitrary 
applications, for now.

> 
>> Long story short: one has to be very careful with that and only enable it for
>> very carefully selected worklads. Letting a workload opt-in on a VMA level is
>> most probably safer than an admin blindly turning this on for random processes
>> ... >>
[...]

>>
>> [1] https://lore.kernel.org/all/20220517092701.1662641-1-xu.xin16@zte.com.cn/
>> [2] https://lore.kernel.org/all/20220609055658.703472-1-xu.xin16@zte.com.cn/
>>
> My understanding is that there were problems with the patch and how it
> exposed KSM. The other objection was the enable-all configuration
> option.

I don't remember all the discussions, but one concern was how to handle 
processes that deliberately want to disable it on some parts of memory.

Anyhow, I cc'ed the relevant parties already.

-- 
Thanks,

David / dhildenb