linux-kernel - Re: [PATCH] x86/speculation/l1tf: suggest what to do on systems with too much RAM

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Message-ID: <20180823154648.GD12066@tassilo.jf.intel.com>
Date:   Thu, 23 Aug 2018 08:46:48 -0700
From:   Andi Kleen <ak@...ux.intel.com>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Michal Hocko <mhocko@...nel.org>, stable@...r.kernel.org,
        Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH] x86/speculation/l1tf: suggest what to do on systems with
 too much RAM

On Thu, Aug 23, 2018 at 04:28:12PM +0200, Vlastimil Babka wrote:
> Two users have reported [1] that they have an "extremely unlikely" system
> with more than MAX_PA/2 memory and L1TF mitigation is not effective. Let's
> make the warning more helpful by suggesting the proper mem=X kernel boot param,
> a rough calculation of how much RAM can be lost (not precise if there's holes
> between MAX_PA/2 and max_pfn in the e820 map) and a link to the L1TF document
> to help decide if the mitigation is worth the unusable RAM.

I'm not sure anyone would really do that. After all you probably prefer
your memory. And if it's really a non ECC client part they are are
already used to to live very dangerously because their undetected RAM bit error
rate will be significant. L1TF is probably one of your smaller problems
in this case...


-Andi