svn commit: r318021 - in head/sys/arm: arm include

[Michal Meloun]

On 09.05.2017 13:34, Andrew Turner wrote:
>> On 9 May 2017, at 12:05, Michal Meloun <mmel at FreeBSD.org> wrote:
>>
>> Author: mmel
>> Date: Tue May  9 11:05:32 2017
>> New Revision: 318021
>> URL: https://svnweb.freebsd.org/changeset/base/318021
>>
>> Log:
>>  Introduce pmap_remap_vm_attr(),
>>  it allows to remap one VM memattr class to another.
>>
>>  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.
 */

>  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 
memory attribute for live memory in SMP system,
without hitting undefined behavior.

Michal