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Re: [RFC PATCH 1/7] x86, mm: ZONE_DEVICE for "device memory"

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On Fri, Aug 14, 2015 at 3:33 PM, Dan Williams <dan.j.williams@intel.com> wrote:
> On Fri, Aug 14, 2015 at 3:06 PM, Jerome Glisse <j.glisse@gmail.com> wrote:
>> On Fri, Aug 14, 2015 at 02:52:15PM -0700, Dan Williams wrote:
>>> On Fri, Aug 14, 2015 at 2:37 PM, Jerome Glisse <j.glisse@gmail.com> wrote:
>>> > On Wed, Aug 12, 2015 at 11:50:05PM -0400, Dan Williams wrote:
> [..]
>>> > What is the rational for not updating max_pfn, max_low_pfn, ... ?
>>> >
>>>
>>> The idea is that this memory is not meant to be available to the page
>>> allocator and should not count as new memory capacity.  We're only
>>> hotplugging it to get struct page coverage.
>>
>> But this sounds bogus to me to rely on max_pfn to stay smaller than
>> first_dev_pfn.  For instance you might plug a device that register
>> dev memory and then some regular memory might be hotplug, effectively
>> updating max_pfn to a value bigger than first_dev_pfn.
>>
>
> True.
>
>> Also i do not think that the buddy allocator use max_pfn or max_low_pfn
>> to consider page/zone for allocation or not.
>
> Yes, I took it out with no effects.  I'll investigate further whether
> we should be touching those variables or not for this new usage.

Although it does not offer perfect protection if device memory is at a
physically lower address than RAM, skipping the update of these
variables does seem to be what we want.  For example /dev/mem would
fail to allow write access to persistent memory if it fails a
valid_phys_addr_range() check.  Since /dev/mem does not know how to
write to PMEM in a reliably persistent way, it should not treat a
PMEM-pfn like RAM.
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[RFC PATCH 1/7] x86, mm: ZONE_DEVICE for "device memory" Dan Williams <dan.j.williams@intel.com> - 2015-08-13 06:00 +0200
  Re: [RFC PATCH 1/7] x86, mm: ZONE_DEVICE for "device memory" Jerome Glisse <j.glisse@gmail.com> - 2015-08-14 23:40 +0200
    Re: [RFC PATCH 1/7] x86, mm: ZONE_DEVICE for "device memory" Dan Williams <dan.j.williams@intel.com> - 2015-08-15 00:00 +0200
      Re: [RFC PATCH 1/7] x86, mm: ZONE_DEVICE for "device memory" Jerome Glisse <j.glisse@gmail.com> - 2015-08-15 00:10 +0200
        Re: [RFC PATCH 1/7] x86, mm: ZONE_DEVICE for "device memory" Dan Williams <dan.j.williams@intel.com> - 2015-08-15 00:40 +0200
          Re: [RFC PATCH 1/7] x86, mm: ZONE_DEVICE for "device memory" Dan Williams <dan.j.williams@intel.com> - 2015-08-15 04:20 +0200
            Re: [RFC PATCH 1/7] x86, mm: ZONE_DEVICE for "device memory" Jerome Glisse <j.glisse@gmail.com> - 2015-08-17 23:50 +0200
              Re: [RFC PATCH 1/7] x86, mm: ZONE_DEVICE for "device memory" Dan Williams <dan.j.williams@intel.com> - 2015-08-18 02:50 +0200
                Re: [RFC PATCH 1/7] x86, mm: ZONE_DEVICE for "device memory" Jerome Glisse <j.glisse@gmail.com> - 2015-08-18 19:00 +0200
                Re: [RFC PATCH 1/7] x86, mm: ZONE_DEVICE for "device memory" Dan Williams <dan.j.williams@intel.com> - 2015-08-18 19:30 +0200
                Re: [RFC PATCH 1/7] x86, mm: ZONE_DEVICE for "device memory" Jerome Glisse <j.glisse@gmail.com> - 2015-08-18 21:10 +0200
      Re: [RFC PATCH 1/7] x86, mm: ZONE_DEVICE for "device memory" Christoph Hellwig <hch@lst.de> - 2015-08-15 11:10 +0200
  Re: [RFC PATCH 1/7] x86, mm: ZONE_DEVICE for "device memory" Christoph Hellwig <hch@lst.de> - 2015-08-15 15:40 +0200

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