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

[Oleksandr Andrushchenko <Oleksandr_Andrushchenko@xxxxxxxx>]

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.
What do I miss here?
>
> Cheers,
>
Thank you,
Oleksandr