From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ed White <edmund.h.white@intel.com>
Subject: Re: Alternate p2m design specification
Date: Wed, 10 Jun 2015 09:39:14 -0700
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To: Jan Beulich <JBeulich@suse.com>
Cc: ravi.sahita@intel.com, Keir Fraser <keir@xen.org>, Ian Campbell <ian.campbell@citrix.com>, Andrew Cooper <andrew.cooper3@citrix.com>, Ian Jackson <ian.jackson@eu.citrix.com>, Tim Deegan <tim@xen.org>, xen-devel@lists.xenproject.org
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On 06/10/2015 12:43 AM, Jan Beulich wrote:
>>>> On 10.06.15 at 02:09, <edmund.h.white@intel.com> wrote:
>> Design
>> ======
> 
> Reads all quite reasonable; just one minor remark:
> 
>> - Core altp2m functionality
>>
>> A new altp2m type is added to the p2m types (in addition to the previous 
>> hostp2m and nestedp2m types). An HVM domain can be started in hostp2m mode 
>> and switched over into altp2m mode via a hypercall. Once a HVM domain is in 
>> altp2m mode, a set of (currently set size is 10) altp2m objects is managed by 
>> Xen.
> 
> Rather than hardcoding 10, how about making the Xen command line
> option specify the value (instead of being a simple boolean one)?
> 
> Jan
> 

For the use cases we're currently aware of, even 10 is generous. I'd be
wary of allowing the user to specify any number up to and including 512
with the current implementation, because there are a number of places where
we do a linear search of the list.

In practice, 1 alternate p2m is not useful, so in a future version of the
code, when we have more idea of how useful people find it, we could say
0=off, 1=on with 10 alternates, any other number=on with that many
alternates.

Does that seem reasonable?

Ed