linux-kernel - Re: [HMM-CDM 0/5] Cache coherent device memory (CDM) with HMM

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Message-ID: <8219f8fb-65bb-7c6b-6c4c-acc0601c1e0f@intel.com>
Date:   Wed, 14 Jun 2017 14:20:23 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Jérôme Glisse <jglisse@...hat.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Cc:     John Hubbard <jhubbard@...dia.com>,
        David Nellans <dnellans@...dia.com>, cgroups@...r.kernel.org,
        Dan Williams <dan.j.williams@...el.com>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Balbir Singh <balbirs@....ibm.com>,
        Aneesh Kumar <aneesh.kumar@...ux.vnet.ibm.com>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [HMM-CDM 0/5] Cache coherent device memory (CDM) with HMM

On 06/14/2017 01:11 PM, Jérôme Glisse wrote:
> Cache coherent device memory apply to architecture with system bus
> like CAPI or CCIX. Device connected to such system bus can expose
> their memory to the system and allow cache coherent access to it
> from the CPU.

How does this interact with device memory that's enumerated in the new
ACPI 6.2 HMAT?  That stuff is also in the normal e820 and, by default,
treated as normal system RAM.  Would this mechanism be used for those
devices as well?

http://www.uefi.org/sites/default/files/resources/ACPI_6_2.pdf