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

On 1/20/2016 11:14 AM, Tian, Kevin wrote:
From: Ian Campbell [mailto:ian.campbell@xxxxxxxxxx]
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

What does "WP" mean? "Write Protected"?


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

I've got no ideas for a better name, "max_ranges" is clearly too generic

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 
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,



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