linux-kernel - Re: [PATCH 1/3] mm: vmalloc: export __vmalloc_node

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Message-ID: <ZpkWj-iFiA-JHbbf@freedom.csh.rit.edu>
Date: Thu, 18 Jul 2024 09:20:15 -0400
From: Mary Strodl <mstrodl@...edom.csh.rit.edu>
To: Matthew Wilcox <willy@...radead.org>
Cc: Christoph Hellwig <hch@...radead.org>,
	Mary Strodl <mstrodl@....rit.edu>, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, urezki@...il.com, linux-mm@...ck.org,
	lee@...nel.org, andi.shyti@...nel.org, linux-i2c@...r.kernel.org,
	s.hauer@...gutronix.de, christian.gmeiner@...il.com
Subject: Re: [PATCH 1/3] mm: vmalloc: export __vmalloc_node_range

On Thu, Jul 18, 2024 at 01:53:23PM +0100, Matthew Wilcox wrote:
> That does work, but I would assume that since this BIOS exists to
> communicate with the hardware that it'd need various special privileges
> and that running in ring 3 would not work.

Exactly.

> Ultimately, better off running the whole thing inside a VM and passing
> the device through to the guest.  Or ignoring the BIOS entirely and
> implementing direct access to the hardware.  But neither of these
> approaches is "a way to do what I'm trying to do", they're entirely
> different approaches to making this hardware work.

If I ran the whole thing inside a VM, I would still need support in the
kernel, right?

As far as I know, there is no documentation on Congatec's side about the
underlying interface. Obviously I could disassemble the blob in the BIOS
and figure it out, but I suspect that will have much less hardware
compatibility and be subject to random breakage if they make a BIOS
update or something. Plus, I would probably run afoul of copyright if I
wrote a driver after doing that.

I'm not really thrilled that this is their design either, but I'm not
sure that there is a better answer...

Thank you!