linux-kernel - Re: l1tf: Kernel suggests I throw away third of my memory. I'd rather not

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Date:   Wed, 17 Oct 2018 15:21:00 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Pavel Machek <pavel@....cz>, Michal Hocko <mhocko@...nel.org>
Cc:     vbabka@...e.cz, hpa@...or.com, torvalds@...ux-foundation.org,
        ak@...ux.intel.com, kernel list <linux-kernel@...r.kernel.org>,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de
Subject: Re: l1tf: Kernel suggests I throw away third of my memory. I'd rather
 not

On 10/17/2018 04:32 AM, Pavel Machek wrote:
>> Well, that depends. Do you care about PROT_NONE attacks as well? If not
>> then no-swap would help you. But even then no-swap is rather theoretical
>> attack on a physical host unless you allow an arbitrary swapout to a
>> malicious user (e.g. allow a user controlled memcg hard limit that would
>> cause excessive local swapouts).
> PROT_NONE attack.. aha, so kernel stores not only information about
> swapped-out pages but also about file-backed pages that are currently
> not present? Hmm. That makes it more complex :-(. 

There are also migration PTE entries that are "swap-like".  They can
exist even if you swapoff -a.

Can we do better?  Sure.  I think we'd all be happy to review patches
that improve the situation if folks have simple ideas for improvement.



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