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

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Message-ID: <Zp5yqoeH752kli8J@freedom.csh.rit.edu>
Date: Mon, 22 Jul 2024 10:54:34 -0400
From: Mary Strodl <mstrodl@...edom.csh.rit.edu>
To: Rudolf Marek <r.marek@...embler.cz>
Cc: Christian Gmeiner <christian.gmeiner@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Matthew Wilcox <willy@...radead.org>,
	Christoph Hellwig <hch@...radead.org>,
	Mary Strodl <mstrodl@....rit.edu>, linux-kernel@...r.kernel.org,
	urezki@...il.com, linux-mm@...ck.org, lee@...nel.org,
	andi.shyti@...nel.org, linux-i2c@...r.kernel.org,
	s.hauer@...gutronix.de
Subject: Re: [PATCH 1/3] mm: vmalloc: export __vmalloc_node_range

On Fri, Jul 19, 2024 at 09:59:37PM +0200, Rudolf Marek wrote:
> I would suggest to simply run the BIOS code of this interface in usermode. Sort of similar to VM86 VESA stuff.
> Last time I looked into this it used STI/CLI/RDMSR/WRMSR and couple of I/O ports and cf8/cfc for PCI.

I took a look at uvesafb (which appears to be what you were talking about) and
it looks like it starts a separate executable and uses some IPC to talk to it.
Is that the best way to do it?

I guess it would look something like:
- driver gets loaded
- driver spawns /sbin/cgeb-helper
- driver uses cn_netlink_send to send the `high_desc` to helper

Then the calls to `board->entry` in the driver get replaced with
`cn_netlink_send` with a `cgeb_fps`.

When the userspace helper gets the message with the `cgeb_fps`, it calls into
the bios code and replies to the driver with send() and passes back cgeb_fps.

>From there, a callback registered with cn_add_callback will pick up the message
and call `wake_up_interruptible` to send the message back to the `cgeb_call`
caller.

Is this what you were imagining? Or is there a simpler way to do it?

Where should the code for the userspace helper live? The vesa stuff appeared to
be out of tree.