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

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Message-ID: <YHBdzPsHantT9r8t@linux.ibm.com>
Date:   Fri, 9 Apr 2021 16:59:40 +0300
From:   Mike Rapoport <rppt@...ux.ibm.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     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

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.

-- 
Sincerely yours,
Mike.