linux-kernel - Re: [HMM v13 07/18] mm/ZONE_DEVICE/x86: add support for un-addressable device memory

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Date:   Mon, 21 Nov 2016 00:08:30 -0500
From:   Jerome Glisse <jglisse@...hat.com>
To:     Balbir Singh <bsingharora@...il.com>
Cc:     akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, John Hubbard <jhubbard@...dia.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [HMM v13 07/18] mm/ZONE_DEVICE/x86: add support for
 un-addressable device memory

On Mon, Nov 21, 2016 at 01:08:56PM +1100, Balbir Singh wrote:
> 
> 
> On 19/11/16 05:18, Jérôme Glisse wrote:
> > It does not need much, just skip populating kernel linear mapping
> > for range of un-addressable device memory (it is pick so that there
> > is no physical memory resource overlapping it). All the logic is in
> > share mm code.
> > 
> > Only support x86-64 as this feature doesn't make much sense with
> > constrained virtual address space of 32bits architecture.
> > 
> 
> Is there a reason this would not work on powerpc64 for example?
> Could you document the limitations -- testing/APIs/missing features?

It should be straight forward for powerpc64, i haven't done it but i
certainly can try to get access to some powerpc64 and add support for
it.

The only thing to do is to avoid creating kernel linear mapping for the
un-addressable memory (just for safety reasons we do not want any read/
write to invalid physical address).

Cheers,
Jérôme