From owner-svn-src-head@freebsd.org  Tue May  9 15:09:09 2017
Return-Path: <owner-svn-src-head@freebsd.org>
Delivered-To: svn-src-head@mailman.ysv.freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org
 [IPv6:2001:1900:2254:206a::19:1])
 by mailman.ysv.freebsd.org (Postfix) with ESMTP id 26299D65561;
 Tue,  9 May 2017 15:09:09 +0000 (UTC)
 (envelope-from andrew@fubar.geek.nz)
Received: from fry.fubar.geek.nz (fry.fubar.geek.nz [139.59.165.16])
 by mx1.freebsd.org (Postfix) with ESMTP id E9FA5935;
 Tue,  9 May 2017 15:09:08 +0000 (UTC)
 (envelope-from andrew@fubar.geek.nz)
Received: from dhcp-10-248-107-222.eduroam.wireless.private.cam.ac.uk
 (global-5-142.nat-2.net.cam.ac.uk [131.111.5.142])
 by fry.fubar.geek.nz (Postfix) with ESMTPSA id 0EC7C4E77F;
 Tue,  9 May 2017 15:09:07 +0000 (UTC)
Content-Type: text/plain; charset=utf-8
Mime-Version: 1.0 (Mac OS X Mail 10.3 \(3273\))
Subject: Re: svn commit: r318021 - in head/sys/arm: arm include
From: Andrew Turner <andrew@fubar.geek.nz>
In-Reply-To: <8fe20c26-3c0c-98ce-227b-740491253047@freebsd.org>
Date: Tue, 9 May 2017 16:09:06 +0100
Cc: src-committers@freebsd.org, svn-src-all@freebsd.org,
 svn-src-head@freebsd.org
Content-Transfer-Encoding: quoted-printable
Message-Id: <CAF5FFE5-4281-4854-AE84-AC60CBF50648@fubar.geek.nz>
References: <201705091105.v49B5WAp097952@repo.freebsd.org>
 <85745E3A-3260-43C7-B134-85BFED786D55@fubar.geek.nz>
 <8fe20c26-3c0c-98ce-227b-740491253047@freebsd.org>
To: mmel@freebsd.org
X-Mailer: Apple Mail (2.3273)
X-BeenThere: svn-src-head@freebsd.org
X-Mailman-Version: 2.1.23
Precedence: list
List-Id: SVN commit messages for the src tree for head/-current
 <svn-src-head.freebsd.org>
List-Unsubscribe: <https://lists.freebsd.org/mailman/options/svn-src-head>,
 <mailto:svn-src-head-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/svn-src-head/>
List-Post: <mailto:svn-src-head@freebsd.org>
List-Help: <mailto:svn-src-head-request@freebsd.org?subject=help>
List-Subscribe: <https://lists.freebsd.org/mailman/listinfo/svn-src-head>,
 <mailto:svn-src-head-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Tue, 09 May 2017 15:09:09 -0000


> On 9 May 2017, at 13:40, Michal Meloun <melounmichal@gmail.com> wrote:
>=20
>=20
>=20
> On 09.05.2017 13:34, Andrew Turner wrote:
>>> On 9 May 2017, at 12:05, Michal Meloun <mmel@FreeBSD.org> wrote:
>>>=20
>>> Author: mmel
>>> Date: Tue May  9 11:05:32 2017
>>> New Revision: 318021
>>> URL: https://svnweb.freebsd.org/changeset/base/318021
>>>=20
>>> Log:
>>> Introduce pmap_remap_vm_attr(),
>>> it allows to remap one VM memattr class to another.
>>>=20
>>> This function is intent to be used as workaround for various SoC =
bugs,
>>> mainly access ordering/sequencing related bugs in crossbar fabric.
>> This seems quite heavy handed to change the attribute for all memory =
of a given type.
> Yes, exactly.  See comment in D10218 -
> /*
> * Workaround for Marvell Armada38X family HW issue
> * between Cortex-A9 CPUs and on-chip devices that may
> * cause hang on heavy load.
> * To avoid that, map all registers including PCIe IO
> * as strongly ordered instead of device memory.
> */

I don=E2=80=99t think it=E2=80=99s been answered if this is just for =
PCIe, or all devices.

>=20
>> Other architectures have pmap_change_attr to change the attribute on =
a specific range of memory.
> Right. Problem is that I don't known any method how we can change=20
> memory attribute for live memory in SMP system,
> without hitting undefined behavior.

I would expect drivers to change the attributes early, before they =
access the memory. We could also use smp_rendezvous to ensure nothing =
else is running, this will have a performance code, however I would not =
expect pmap_change_attr to be used in the fast path.

Andrew