Re: [PATCH v7] RISC-V: enable XIP

David Hildenbrand
2021-04-09T14:10:38Z

> Am 09.04.2021 um 15:59 schrieb Mike Rapoport <rppt@linux.ibm.com>:
>
> ﻿On Fri, Apr 09, 2021 at 02:46:17PM +0200, David Hildenbrand wrote:
>>>>> Also, will that memory properly be exposed in the resource tree as
>>>>> System RAM (e.g., /proc/iomem) ? Otherwise some things (/proc/kcore)
>>>>> won't work as expected - the kernel won't be included in a dump.
>>> Do we really need a XIP kernel to included in kdump?
>>> And does not it sound weird to expose flash as System RAM in /proc/iomem? ;-)
>>
>> See my other mail, maybe we actually want something different.
>>
>>>
>>>> I have just checked and it does not appear in /proc/iomem.
>>>>
>>>> Ok your conclusion would be to have struct page, I'm going to implement this
>>>> version then using memblock as you described.
>>>
>>> I'm not sure this is required. With XIP kernel text never gets into RAM, so
>>> it does not seem to require struct page.
>>>
>>> XIP by definition has some limitations relatively to "normal" operation,
>>> so lack of kdump could be one of them.
>>
>> I agree.
>>
>>>
>>> I might be wrong, but IMHO, artificially creating a memory map for part of
>>> flash would cause more problems in the long run.
>>
>> Can you elaborate?
>
> Nothing particular, just a gut feeling. Usually, when you force something
> it comes out the wrong way later.
>
>>>
>>> BTW, how does XIP account the kernel text on other architectures that
>>> implement it?
>>
>> Interesting point, I thought XIP would be something new on RISC-V (well, at
>> least to me :) ). If that concept exists already, we better mimic what
>> existing implementations do.
>
> I had quick glance at ARM, it seems that kernel text does not have memory
> map and does not show up in System RAM.
>

Does it show up in a different way or not at all?

> --
> Sincerely yours,
> Mike.
>