Re: HVMlite ABI specification DRAFT A

["Roger Pau Monné" <roger.pau@citrix.com>]

El 5/2/16 a les 16:29, Jan Beulich ha escrit:
>>>> On 05.02.16 at 16:00, <roger.pau@citrix.com> wrote:
>> El 5/2/16 a les 15:31, Jan Beulich ha escrit:
>>>>>> On 05.02.16 at 15:27, <roger.pau@citrix.com> wrote:
>>>> El 5/2/16 a les 14:22, Jan Beulich ha escrit:
>>>>> Also consider e.g. the device IRQ which the
>>>>> serial driver may be using: We specifically suppress modifications to
>>>>> RTEs for in-use IRQs in current code and would of course need to
>>>>> do so in the PVHv2 code too. That way there would be no proper
>>>>> way to establish the two bits (short of grabbing the data from what
>>>>> Dom0 tries to write despite us otherwise suppressing the write).
>>>>
>>>> For devices in use by Xen itself, like the uart, doesn't Xen already
>>>> take care of setting the right interrupt configuration? Or else how does
>>>> the uart work before Dom0 is launched?
>>>
>>> In polling mode.
>>
>> I guess this is not very common, since most uarts use a GSI < 16. In
>> which case, couldn't the ones that use a GSI >= 16 just be used in
>> polling mode _forever_?
> 
> It could, but it's inefficient.
> 
>>>> The plan was to use the STAO ACPI table in order to notify Dom0 that
>>>> certain devices (like the uart) are not accessible, thus preventing Dom0
>>>> from setting any interrupts for this devices at all (ie: they should
>>>> just be ignored/skipped by Dom0 when doing device enumeration).
>>>>
>>>> And in any case, writes to pins that are in use by Xen should not be
>>>> propagated to the physical IO APIC at all, since I would assume Xen has
>>>> already set them up properly.
>>>
>>> Once again - it can't without Dom0's help if the interrupt isn't in
>>> the legacy GSI range (below 16).
>>
>> Which devices is Xen expected to use with a GSI >= 16? I can only think
>> of the uart, but maybe there are others which I'm missing?
> 
> Right now only the UART, but who knows what's to come?

TBH (and maybe I'm being overly confident here) I expect that anything
new will just use MSI.

Roger.