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

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Message-Id: <F096121C-8F7A-4E9A-B319-2C5F656610EA@redhat.com>
Date:   Fri, 9 Apr 2021 16:10:15 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Mike Rapoport <rppt@...ux.ibm.com>
Cc:     David Hildenbrand <david@...hat.com>, Alex Ghiti <alex@...ti.fr>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-mm@...ck.org,
        Vitaly Wool <vitaly.wool@...sulko.com>
Subject: Re: [PATCH v7] RISC-V: enable XIP


> Am 09.04.2021 um 15:59 schrieb Mike Rapoport <rppt@...ux.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.
>