Re: [PATCH v6 01/13] xen/pci: arm: add stub for is_memory_hole

[Julien Grall <julien@xxxxxxx>]

On 04/02/2022 10:35, Oleksandr Andrushchenko wrote:
> On 04.02.22 11:57, Julien Grall wrote:
> > Hi,
> >
> > On 04/02/2022 09:47, Oleksandr Andrushchenko wrote:
> > > > > Could you please help me with the exact message you would like to see?
> > > > 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.
> > > >
> > > > If we were going to go this route, I would also rename the function to be 
> > > > better match what it is doing (i.e. it checks the BAR is correctly placed). As 
> > > > a potentially optimization/hardening for Arm, we could pass the hostbridge so 
> > > > we don't have to walk all of them.
> > > It seems this needs to live in the commit message then? So, it is easy to find
> > > as everything after "---" is going to be dropped on commit
> > I expect the function to be fully implemented before this is will be merged.
> >
> > So if it is fully implemented, then a fair chunk of what I wrote would not be 
> > necessary to carry in the commit message.
> Well, we started from that we want *something* with TODO and now
> you request it to be fully implemented before it is merged.
I don't think I ever suggested this patch would be merged as-is. Sorry 
if this may have crossed like this.
Instead, my intent by asking you to send a TODO patch is to start a 
discussion how this function could be implemented for Arm.
You sent a TODO but you didn't provide any summary on what is the issue, 
what we want to achieve... Hence my request to add a bit more details so 
the other reviewers can provide their opinion more easily.
Cheers,

--
Julien Grall