linux-kernel - Re: [LSF/MM] CXL Boot to Bash - Section 0a: CFMWS and NUMA Flexiblity

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Message-ID: <Z9QzQEzcpHjZQI7U@gourry-fedora-PF4VCD3F>
Date: Fri, 14 Mar 2025 09:46:40 -0400
From: Gregory Price <gourry@...rry.net>
To: Jonathan Cameron <Jonathan.Cameron@...wei.com>
Cc: lsf-pc@...ts.linux-foundation.org, linux-mm@...ck.org,
	linux-cxl@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [LSF/MM] CXL Boot to Bash - Section 0a: CFMWS and NUMA Flexiblity

On Fri, Mar 14, 2025 at 11:09:42AM +0000, Jonathan Cameron wrote:
> > 
> > I was unaware that we blocked mapping persistent as volatile.  I was
> > working off the assumption that could be flexible mapped similar to...
> > er... older, non-cxl hardware... cough.
> 
> You can use it as volatile, but that doesn't mean we allow it in a CFMWS
> that says the host PA range is not suitable for persistent.
> A BIOS might though I think.
>

aaaaaaaaaaaaah this helps.  Ok, we can repurpose the hardware, but not
the CFMWS.  Even more pressure on platforms to get it right :P.

> > 
> > Along with the above note, and as mentioned on discord, I think this
> > whole section naturally evolves into a library of "Sane configurations"
> > and "We promise nothing for `reasons`" configurations.
> 
> :)  Snag is that as Dan pointed out on discord we assume this applies
> even without the lock.  So it is possible to have device and host 
> hardware combinations where things are forced to be very non-intuitive.
>

Right, but i think that falls into "We promise nothing, for `reasons`".

At the very least it would give us a communication tool that helps
bridge the gap between platform, linux, and end-users.

Or it'd just makes it all worse, one of the two.

~Gregory