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

[Juerg Haefliger]

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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