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Re: [PATCH v5 01/11] xen/arm: xc_domain_ioport_permission(..) not supported on ARM.

  • To: Bertrand Marquis <bertrand.marquis@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
  • From: Oleksandr Andrushchenko <Oleksandr_Andrushchenko@xxxxxxxx>
  • Date: Mon, 11 Oct 2021 14:16:09 +0000
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  • Cc: Rahul Singh <rahul.singh@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Andre Przywara <Andre.Przywara@xxxxxxx>, Ian Jackson <iwj@xxxxxxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>
  • Delivery-date: Mon, 11 Oct 2021 14:16:23 +0000
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  • Thread-topic: [PATCH v5 01/11] xen/arm: xc_domain_ioport_permission(..) not supported on ARM.

Hi, all

On 11.10.21 16:40, Bertrand Marquis wrote:
> Hi Roger,
> + Oleksandr to have a better PCI expert then me.
>> On 11 Oct 2021, at 14:20, Roger Pau Monné <roger.pau@xxxxxxxxxx> wrote:
>> On Mon, Oct 11, 2021 at 12:11:04PM +0000, Bertrand Marquis wrote:
>>> Hi Roger,
>>>> On 11 Oct 2021, at 12:47, Roger Pau Monné <roger.pau@xxxxxxxxxx> wrote:
>>>> On Wed, Oct 06, 2021 at 06:40:27PM +0100, Rahul Singh wrote:
>>>>> ARM architecture does not implement I/O ports. Ignore this call on ARM
>>>>> to avoid the overhead of making a hypercall just for Xen to return
>>>>> -ENOSYS.
>>>> What is the cal trace of this function actually on Arm?
>>>> AFAICT libxl will only call xc_domain_ioport_permission if there are
>>>> IO ports explicitly defined in the guest configuration, or if any of
>>>> the BARs of the PCI device is in the IO space, which is not possible
>>>> on Arm.
>>> PCI devices BARs can be in the IO space as the PCI devices are not
>>> Arm specific. There is not ioports on arm so to be used those can be
>>> in some cases remapped and accessed as MMIOs or are not possible
>>> to use at all.
>>> But the IO space does appear when BARs are listed even on Arm.
>> Urg, I wonder whether those devices with IO BARs will work correctly
>> under Arm then.
>> How do you know whether the BAR has been remapped from IO space into
>> MMIO?
> We cannot, I think the platform will define if this is the case and where.
> @oleksandr: I remember that this was discussed during some of our
> meetings but I have no idea of the details here, can you help ?
For the guest domains we emulate a host bridge without IO, so the
guest won't be able to assign any IO memory at all.



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