From mboxrd@z Thu Jan  1 00:00:00 1970
From: George Dunlap <George.Dunlap@eu.citrix.com>
Subject: Re: [PATCH for-4.5 v6 00/16] Xen VMware tools support
Date: Tue, 23 Sep 2014 13:35:27 +0100
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To: Ian Campbell <Ian.Campbell@citrix.com>
Cc: Kevin Tian <kevin.tian@intel.com>, Keir Fraser <keir@xen.org>, Jun Nakajima <jun.nakajima@intel.com>, Stefano Stabellini <stefano.stabellini@eu.citrix.com>, Ian Jackson <ian.jackson@eu.citrix.com>, Eddie Dong <eddie.dong@intel.com>, Don Slutz <dslutz@verizon.com>, Tim Deegan <tim@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>, "xen-devel@lists.xen.org" <xen-devel@lists.xen.org>, Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
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On Tue, Sep 23, 2014 at 1:30 PM, Ian Campbell <Ian.Campbell@citrix.com> wrote:
> On Mon, 2014-09-22 at 13:19 -0400, Don Slutz wrote:
>> >> It sounds plausible, for sure.
>> >>
>> >> Even so, why can't the result of that #GP be a calldown into qemu for
>> >> further processing?
>> >
>>
>> This is not simple in that QEMU does not have access to the VCPU
>> registers.  Unlike a normal
>> I/O request, vmware_port (aka vmport) both reads and writes VCPU registers.
>
> Are you saying that emulating a normal in or out instruction doesn't
> require accessing vcpu registers? Are you sure? Surely it needs to
> either read the source or write the destination register somehow.

At the moment Xen does all of the decoding of instructions; what it
sends to qemu is just "Read / Write X bytes at address Y" (along with
data when appropriate).  Qemu doesn't require access to the registers.

 -George