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

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Message-ID: <c3d8e978-6db2-6637-8a88-e6c1acc2b854@suse.cz>
Date:   Wed, 17 Oct 2018 16:13:13 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Andi Kleen <ak@...ux.intel.com>, Pavel Machek <pavel@....cz>
Cc:     mhocko@...e.com, hpa@...or.com, torvalds@...ux-foundation.org,
        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 10/17/18 4:08 PM, Andi Kleen wrote:
> On Wed, Oct 17, 2018 at 12:56:10PM +0200, Pavel Machek wrote:
>> Hi!
>>
>> 6a012288 suggests I throw away 1GB on RAM. On 3GB system.. that is not
>> going to be pleasant.
> 
> Just rebuild your kernel with PAE? I assume your CPU supports it.

I think it is built with PAE or this would kick in:

#if CONFIG_PGTABLE_LEVELS == 2
        pr_warn("Kernel not compiled for PAE. No mitigation for L1TF\n");
        return;
#endif

I.e. no MAX_PA/2 messages.

> This will also give you NX, which if you're really worried
> about security is far more important than L1TF.
> 
> If you don't worry about security just ignore.
> 
> -Andi
>