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Re: [Xen-devel] [PATCH v9 12/14] tools/libxl: read from config if passing through primary GPU

>>> On 03.07.14 at 12:49, <linux@xxxxxxxxxxxxxx> wrote:

> Thursday, July 3, 2014, 12:30:13 PM, you wrote:
>>>>> On 02.07.14 at 21:00, <linux@xxxxxxxxxxxxxx> wrote:
>>> Wednesday, July 2, 2014, 8:42:21 PM, you wrote:
>>>> --- a/docs/man/xl.cfg.pod.5
>>>> +++ b/docs/man/xl.cfg.pod.5
>>>> @@ -601,6 +601,13 @@ More information about Xen gfx_passthru feature is 
> available
>>>>  on the XenVGAPassthrough L<http://wiki.xen.org/wiki/XenVGAPassthrough>
>>>>  wiki page.
>>>> +=item B<gfx_passthru_primary=BOOLEAN>
>>>> +
>>>> +If set to true, indicates that one of the GPUs passed through to the
>>>> +domain is the primary one; therefore allows to the domain's stubdoman
>>>> +access permissions for the VGA framebuffer. Note that this option
>>>> +defaults to true.
>>>> +
>>> Wouldn't it make sense to make it a pci <BDF> instead of boolean, 
>>> so that instead of: "one of the GPU's passed is the primary",
>>> you could actually specify: "this *specific* GPU passed through i would 
>>> like 
>>> to be the primary" ?
>> No. You can't just make some card primary (with "primary" really
>> meaning accessible via the legacy VGA interface). Within a host
>> there's exactly one card that can be primary. If that card gets
>> passed through, it can also be primary in the guest. Any other
>> card, not having the legacy VGA ports routed through the
>> corresponding circuitry, can't all of the sudden become the
>> primary one in a guest.
> Is that also true for a HVM guest ?
> - aren't the legacy VGA ports emulated without passthrough (by hvmloader / 
>   seabios, with the cirrus or stdvga)

Sure, but we're only talking about a passed through card here.

> - couldn't they be rerouted to a device that is passed through ?

No idea how you imagine to do that.

> Or would that make the VGA card do legacy stuff on the host instead of in 
> the 
> guest (since it's lowlevel legacy stuff) ?

Depends on whose port space you think of.


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