linux-kernel - Re: [kernel-hardening] [RFC PATCH v2 2/3] xpfo: Only put previous userspace pages into the hot cache

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Message-ID: <7badeb6c-e343-4327-29ed-f9c9c0b6654b@hpe.com>
Date:   Wed, 14 Sep 2016 16:40:49 +0200
From:   Juerg Haefliger <juerg.haefliger@....com>
To:     Dave Hansen <dave.hansen@...el.com>,
        kernel-hardening@...ts.openwall.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-x86_64@...r.kernel.org
Cc:     vpk@...columbia.edu
Subject: Re: [kernel-hardening] [RFC PATCH v2 2/3] xpfo: Only put previous
 userspace pages into the hot cache

Hi Dave,

On 09/14/2016 04:33 PM, Dave Hansen wrote:
> On 09/14/2016 12:19 AM, Juerg Haefliger wrote:
>> Allocating a page to userspace that was previously allocated to the
>> kernel requires an expensive TLB shootdown. To minimize this, we only
>> put non-kernel pages into the hot cache to favor their allocation.
> 
> Hi, I had some questions about this the last time you posted it.  Maybe
> you want to address them now.

I did reply: https://lkml.org/lkml/2016/9/5/249

...Juerg


> --
> 
> But kernel allocations do allocate from these pools, right?  Does this
> just mean that kernel allocations usually have to pay the penalty to
> convert a page?
> 
> So, what's the logic here?  You're assuming that order-0 kernel
> allocations are more rare than allocations for userspace?
> 




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