Re: [PATCH V7 01/11] xen/pci: arm: add stub for is_memory_hole

[Oleksandr <olekstysh@xxxxxxxxx>]

On 03.08.22 12:29, Rahul Singh wrote:
> Hi Oleksandr,

Hello Rahul


> > On 29 Jul 2022, at 5:28 pm, Oleksandr <olekstysh@xxxxxxxxx> wrote:
> >
> >
> > Hello Rahul
> >
> >
> > On 19.07.22 20:42, Oleksandr Tyshchenko wrote:
> > > From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
> > >
> > > Add a stub for is_memory_hole which is required for PCI passthrough
> > > on Arm.
> > >
> > > Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
> > > ---
> > > OT: It looks like the discussion got stuck. As I understand this
> > > patch is not immediately needed in the context of current series
> > > as PCI passthrough is not enabled on Arm at the moment. So the patch
> > > could be added later on, but it is needed to allow PCI passthrough
> > > to be built on Arm for those who want to test it.
> > >
> > > Copy here some context provided by Julien:
> > >
> > > Here a summary of the discussion (+ some my follow-up thoughts):
> > >
> > > is_memory_hole() was recently introduced on x86 (see commit 75cc460a1b8c
> > > "xen/pci: detect when BARs are not suitably positioned") to check
> > > whether the BAR are positioned outside of a valid memory range. This was
> > > introduced to work-around quirky firmware.
> > >
> > > In theory, this could also happen on Arm. In practice, this may not
> > > happen but it sounds better to sanity check that the BAR contains
> > > "valid" I/O range.
> > >
> > > On x86, this is implemented by checking the region is not described is
> > > in the e820. IIUC, on Arm, the BARs have to be positioned in pre-defined
> > > ranges. So I think it would be possible to implement is_memory_hole() by
> > > going through the list of hostbridges and check the ranges.
> > >
> > > But first, I'd like to confirm my understanding with Rahul, and others.
> > May I please ask about your opinion on that?
> I agree with Julien we can implement the something similar to is_memory_hole()  
> for ARM
> that will check that the bar is within the bridge ranges.
>
> If you are okay you can discard this patch in next version of the series and I 
> will push the patch
> for review.
Perfect! Thank you, that would be much appreciated!


> Regards,
> Rahul
--
Regards,

Oleksandr Tyshchenko