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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>
- From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Date: Mon, 11 Oct 2021 15:20:54 +0200
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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 13:21:45 +0000
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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?
IMO instead of faking a successful return value from
xc_domain_ioport_permission we should avoid the call completely in the
first place, specially if we need to instead issue a call to
xc_domain_iomem_permission.
Thanks, Roger.
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