Re: [Xen-devel] [PATCH for-4.5 v6 00/16] Xen VMware tools support

[George Dunlap <George.Dunlap@xxxxxxxxxxxxx>]

On Tue, Sep 23, 2014 at 1:30 PM, Ian Campbell <Ian.Campbell@xxxxxxxxxx> 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

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