linux-kernel - Re: [RFD] clear virtual machine memory when virtual machine is turned off

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Message-ID: <d5d854de-d59d-47d5-35ce-fe3a924a5a93@redhat.com>
Date:   Fri, 3 Dec 2021 19:20:12 +0100
From:   David Hildenbrand <david@...hat.com>
To:     fei luo <morphyluo@...il.com>
Cc:     akpm@...ux-foundation.org, mike.kravetz@...cle.com, arnd@...db.de,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, xiaofeng.yan2012@...il.com
Subject: Re: [RFD] clear virtual machine memory when virtual machine is turned
 off

> Yes, this feature needs to consider when page migration, the content
> of the old page needs to be cleared, and the swap space needs to
> be cleared before swap. Of course, for security reasons, swap can be
> prohibited. Here I just listed some of the changes involved, not all
> aspects. This feature is mainly aimed at clearing the memory of
> the virtual machine after shutdown, so it is more aimed at anonymous
> mapping and huge page mapping
> 
>>>
>>>
>>> When reusing the page that has been cleared, there is no need to clear it
>>>
>>> again, which also speeds up the memory allocation of user-mode programs.
>>>
>>>
>>> Is this feature feasible?
>>
>> "init_on_free=1" for the system as a whole, which might sounds like what
>> might tackle part of your use case.
>>
> 
> This feature is mainly to prevent the used memory information from leaking,
> not to clear the memory before use.

That's the whole purpose of init_on_free -- maybe you should give that a
second look.

I don't think MAP_UNMAPZERO is what we want.

-- 
Thanks,

David / dhildenb