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

From	Dave Hansen <dave.hansen@intel.com>
Newsgroups	linux.kernel
Subject	Re: [kernel-hardening] [RFC PATCH v2 2/3] xpfo: Only put previous userspace pages into the hot cache
Date	2016-09-14 16:50 +0200
Message-ID	<shjFE-24s-45@gated-at.bofh.it> (permalink)
References	<scUZc-7lv-9@gated-at.bofh.it> <shcEa-6cS-9@gated-at.bofh.it> <shcEa-6cS-11@gated-at.bofh.it> <shjvY-215-23@gated-at.bofh.it> <shjFE-24s-25@gated-at.bofh.it>
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> On 09/02/2016 10:39 PM, Dave Hansen wrote:
>> On 09/02/2016 04:39 AM, Juerg Haefliger wrote:
>> Does this
>> just mean that kernel allocations usually have to pay the penalty to
>> convert a page?
> 
> Only pages that are allocated for userspace (gfp & GFP_HIGHUSER == GFP_HIGHUSER) which were
> previously allocated for the kernel (gfp & GFP_HIGHUSER != GFP_HIGHUSER) have to pay the penalty.
> 
>> So, what's the logic here?  You're assuming that order-0 kernel
>> allocations are more rare than allocations for userspace?
> 
> The logic is to put reclaimed kernel pages into the cold cache to
> postpone their allocation as long as possible to minimize (potential)
> TLB flushes.

OK, but if we put them in the cold area but kernel allocations pull them
from the hot cache, aren't we virtually guaranteeing that kernel
allocations will have to to TLB shootdown to convert a page?

It seems like you also need to convert all kernel allocations to pull
from the cold area.

Thread

[RFC PATCH v2 0/3] Add support for eXclusive Page Frame Ownership (XPFO) Juerg Haefliger <juerg.haefliger@hpe.com> - 2016-09-14 09:20 +0200
  [RFC PATCH v2 3/3] block: Always use a bounce buffer when XPFO is enabled Juerg Haefliger <juerg.haefliger@hpe.com> - 2016-09-14 09:20 +0200
    Re: [RFC PATCH v2 3/3] block: Always use a bounce buffer when XPFO  is enabled Christoph Hellwig <hch@infradead.org> - 2016-09-14 09:40 +0200
  [RFC PATCH v2 2/3] xpfo: Only put previous userspace pages into the hot cache Juerg Haefliger <juerg.haefliger@hpe.com> - 2016-09-14 09:20 +0200
    Re: [kernel-hardening] [RFC PATCH v2 2/3] xpfo: Only put previous  userspace pages into the hot cache Dave Hansen <dave.hansen@intel.com> - 2016-09-14 16:40 +0200
      Re: [kernel-hardening] [RFC PATCH v2 2/3] xpfo: Only put previous  userspace pages into the hot cache Juerg Haefliger <juerg.haefliger@hpe.com> - 2016-09-14 16:50 +0200
        Re: [kernel-hardening] [RFC PATCH v2 2/3] xpfo: Only put previous  userspace pages into the hot cache Dave Hansen <dave.hansen@intel.com> - 2016-09-14 16:50 +0200
          Re: [kernel-hardening] [RFC PATCH v2 2/3] xpfo: Only put previous  userspace pages into the hot cache Juerg Haefliger <juerg.haefliger@hpe.com> - 2016-09-21 07:40 +0200
  [RFC PATCH v2 1/3] Add support for eXclusive Page Frame Ownership (XPFO) Juerg Haefliger <juerg.haefliger@hpe.com> - 2016-09-14 09:20 +0200
  Re: [RFC PATCH v2 0/3] Add support for eXclusive Page Frame Ownership  (XPFO) Juerg Haefliger <juerg.haefliger@hpe.com> - 2016-09-14 09:30 +0200
  Re: [kernel-hardening] [RFC PATCH v2 0/3] Add support for eXclusive  Page Frame Ownership (XPFO) Mark Rutland <mark.rutland@arm.com> - 2016-09-14 11:40 +0200
    Re: [kernel-hardening] [RFC PATCH v2 0/3] Add support for eXclusive  Page Frame Ownership (XPFO) Mark Rutland <mark.rutland@arm.com> - 2016-09-14 11:50 +0200

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