Re: [PATCH] cxl: Update Soft Reserved resources upon region creation

[Dan Williams <dan.j.williams@intel.com>]

Dan Williams wrote:
> Nathan Fontenot wrote:
> > Update handling of SOFT RESERVE iomem resources that intersect with
> > CXL region resources to remove the intersections from the SOFT RESERVE
> > resources. The current approach of leaving the SOFT RESERVE
> > resource as is can cause failures during hotplug replace of CXL
> > devices because the resource is not available for reuse after
> > teardown of the CXL device.
> > 
> > The approach is to trim out any pieces of SOFT RESERVE resources
> > that intersect CXL regions. To do this, first set aside any SOFT RESERVE
> > resources that intersect with a CFMWS into a separate resource tree
> > during e820__reserve_resources_late() that would have been otherwise
> > added to the iomem resource tree.
> > 
> > As CXL regions are created the cxl resource created for the new
> > region is used to trim intersections from the SOFT RESERVE
> > resources that were previously set aside.
> > 
> > Once CXL device probe has completed ant remaining SOFT RESERVE resources
> > remaining are added to the iomem resource tree. As each resource
> > is added to the oiomem resource tree a new notifier chain is invoked
> > to notify the dax driver of newly added SOFT RESERVE resources so that
> > the dax driver can consume them.
> 
> Hi Nathan, this patch hit on all the mechanisms I would expect, but upon
> reading it there is an opportunity to zoom out and do something blunter
> than the surgical precision of this current proposal.

Note that the reason I have new / enhanced focus on simplicity is that
this mechanism is probably our only way to resolve regressions like
this:

http://lore.kernel.org/d8d2c310-2021-431f-adbe-71ad0a17896a@amd.com

In other words, mainline is now failing to enumerate memory in more
scenarios than it was previously. I do not want to be forcing Linus and
the -stable team to to review wider changes to kernel/resource.c than is
necessary. I.e. there is a chance this proposal needs to be seek a
v6.13-rc consideration.