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

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Date:   Wed, 14 Sep 2016 07:33:07 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     kernel-hardening@...ts.openwall.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-x86_64@...r.kernel.org
Cc:     juerg.haefliger@....com, vpk@...columbia.edu
Subject: Re: [kernel-hardening] [RFC PATCH v2 2/3] xpfo: Only put previous
 userspace pages into the hot cache

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.

--

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?