From mboxrd@z Thu Jan  1 00:00:00 1970
From: Don Slutz <dslutz@verizon.com>
Subject: Re: [PATCH for-4.5 v6 08/16] xen: Add limited support
 of VMware's hyper-call rpc
Date: Mon, 22 Sep 2014 17:18:54 -0400
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To: Ian Campbell <Ian.Campbell@citrix.com>, Don Slutz <dslutz@verizon.com>
Cc: Tim Deegan <tim@xen.org>, Kevin Tian <kevin.tian@intel.com>, Keir Fraser <keir@xen.org>, Jun Nakajima <jun.nakajima@intel.com>, Stefano Stabellini <stefano.stabellini@eu.citrix.com>, George Dunlap <George.Dunlap@eu.citrix.com>, Ian Jackson <ian.jackson@eu.citrix.com>, Eddie Dong <eddie.dong@intel.com>, xen-devel@lists.xen.org, Aravind Gopalakrishnan <Aravind.Gopalakrishnan@amd.com>, Jan Beulich <jbeulich@suse.com>, Andrew Cooper <andrew.cooper3@citrix.com>, Boris Ostrovsky <boris.ostrovsky@oracle.com>, Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
List-Id: xen-devel@lists.xenproject.org


On 09/22/14 09:47, Ian Campbell wrote:
> On Sat, 2014-09-20 at 14:07 -0400, Don Slutz wrote:
>> This interface is an extension of __HYPERVISOR_HVM_op.  It was
>> picked because xc_get_hvm_param() also uses it and VMware guest
>> info is a lot like a hvm param.
> Sorry if this has been discussed before, but did you consider doing all
> this in qemu rather than Xen?


Yes, but QEMU does not have access to the VCPU registers.  Also QEMU 
does not have this code; so would also need it to be added.

A second part would be adding a way for a tool stack to
communicate with QEMU to access this data.  xenstore/xenbus might
be one way to do this.

> Unless there are frequent accesses to these things then qemu would be
> the default best place for this sort of thing, especially since as
> you've observed there is some pretty complex memory management and
> string handling which it would generally be better to avoid in the
> hypervisor.

The more complex memory management is around not using the
heap during a single guest instruction (inl (%dx)).  Handling
migration of a fully variable sized hunk is not that simple.

Also preventing the guest from accessing outside of the defined
memory does increase the complexity.


> Your description of HVM_PARAM_VMPORT_RESET_TIME suggests they aren't
> typically accessed very frequently.

The rate I have seen is a low number per minute.  However there
is nothing that prevents a guest from doing a very high rate.

     -Don Slutz

> Ian.
>