Re: [PATCH 3/3] tools: introduce parameter max_ranges.

From: "Yu, Zhang" <yu.c.zhang@linux.intel.com>
To: "Tian, Kevin" <kevin.tian@intel.com>,
	Ian Campbell <ian.campbell@citrix.com>,
	Wei Liu <wei.liu2@citrix.com>,
	Paul Durrant <Paul.Durrant@citrix.com>
Cc: "Keir (Xen.org)" <keir@xen.org>,
	Andrew Cooper <Andrew.Cooper3@citrix.com>,
	"xen-devel@lists.xen.org" <xen-devel@lists.xen.org>,
	Stefano Stabellini <Stefano.Stabellini@citrix.com>,
	"Lv, Zhiyuan" <zhiyuan.lv@intel.com>,
	"jbeulich@suse.com" <jbeulich@suse.com>
Subject: Re: [PATCH 3/3] tools: introduce parameter max_ranges.
Date: Wed, 20 Jan 2016 11:33:28 +0800	[thread overview]
Message-ID: <569F0008.1010201@linux.intel.com> (raw)
In-Reply-To: <AADFC41AFE54684AB9EE6CBC0274A5D15F7860BF@SHSMSX101.ccr.corp.intel.com>


On 1/20/2016 11:14 AM, Tian, Kevin wrote:
>> From: Ian Campbell [mailto:ian.campbell@citrix.com]
>> Sent: Tuesday, January 19, 2016 11:19 PM
>>
>> On Tue, 2016-01-19 at 15:04 +0000, Wei Liu wrote:
>>
>> This patch doesn't seem to have been CCd to the tools maintainers, adding
>> Ian too, I think everyone else was picked up along the way.
>>
>> Please use ./scripts/get_maintainers.pl in the future.
>>
>>> On Tue, Jan 19, 2016 at 02:47:40PM +0000, Paul Durrant wrote:
>>> [...]
>>>>> ranges so perhaps the parameter name could be
>>>>> 'max_wp_memory_ranges'?
>>>>>>
>>>>>
>>>>> What does "WP" mean? "Write Protected"?
>>>>>
>>>>
>>>> Yes.
>>>>
>>>>> Is this parameter closely related to IOREQ server? Should it contain
>>>>> "ioreq" somehow?
>>>>>
>>>>
>>>> It is closely related but ioreq server is an implementation detail so
>>>> do we want to expose it as a tunable? The concept we need to capture
>>>> is that the toolstack can tune the limit of the maximum number of
>>>> pages in the VM that can be set such that writes are emulated (but
>>>> reads are as for normal ram). Or I guess we could get very specific
>>>> and call it something like 'max_gtt_shadows'?
>>>
>>> I would prefer generic concept in this case ("wp"). Let's wait a bit for
>>> other people to voice their opinion.
>>>
>>> Whichever one we pick it the meaning of the acronym needs to be clearly
>>> documented...
>>
>> I've got no ideas for a better name, "max_ranges" is clearly too generic
>> though.
>>
>> One thought -- does XenGT require some other configuration option to enable
>> it or maybe a privilege which the target domain must necessarily have?
>> Could we use something like one of those to cause the t/stack to just DTRT
>> without the user having to micromanage the amount of pages which are
>> allowed to have this property?
>>
>
> Using "wp" is clear to me.
>
Thank you all. :)
So how about "max_wp_ram_ranges"? And the "wp" shall be well explained 
in documentation.

> As a feature this write-protection has nothing to be GPU virtualization specific.
> In the future the same mediated pass-through idea used in XenGT may be
> used on other I/O devices which need to shadow some structure w/ requirement
> to write-protect guest memory. So it's not good to tie this to either XenGT
> or GTT.
>
Thank you, Kevin.
Well, if this parameter is not supposed to be xengt specific, we do not 
need to connect it with any xengt flag such as ."vgt=1" or "GVT-g=1". 
Hence the user will have to configure the max_wp_ram_ranges himself,
right?

B.R.
Yu

> Thanks
> Kevin
>