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

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Message-ID: <20181017121705.GQ18839@dhcp22.suse.cz>
Date:   Wed, 17 Oct 2018 14:17:05 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Pavel Machek <pavel@....cz>
Cc:     vbabka@...e.cz, hpa@...or.com, torvalds@...ux-foundation.org,
        ak@...ux.intel.com, dave.hansen@...el.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 Wed 17-10-18 13:32:26, Pavel Machek wrote:
[...]
> > > Now question is... can we do better? Kernel stores information about
> > > swapped-out pages there, right? That sounds like a cool hack, but
> > > maybe it is time to get rid of that hack?
> > 
> > Patches are welcome.
> 
> Cooperation will be needed if you want to see patches. As
> in... answering the questions above.

The question is whether that is really worth it. L1TF is mostly about
virtual environments. If you are running in a native HW then I wouldn't
lose much sleep over it. a) pfns stored in PROT_NONE entries are
controlled by the OS b) swap based attacks with something interesting in
L1$ colliding with the swap entry is theoretical at best.
-- 
Michal Hocko
SUSE Labs