Re: [PATCH 1/3] mm: vmalloc: export __vmalloc_node_range

Mary Strodl
2024-07-22T14:54:42Z

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.