On Tue, Jan 21, 2025 at 12:57:19PM -0600, Fontenot, Nathan wrote: > > > On 1/21/2025 2:19 AM, David Hildenbrand wrote: > > On 16.01.25 18:42, Nathan Fontenot wrote: > > > > Hi, > > > >> Introduce the ability to manage SOFT RESERVED kernel resources prior to > >> these resources being placed in the iomem resource tree. This provides > >> the ability for drivers to update SOFT RESERVED resources that intersect > >> with their memory resources. > >> > >> During boot, any resources marked as IORES_DESC_SOFT_RESERVED are placed > >> on the soft reserve resource tree. Once boot completes all resources > >> are placed on the iomem resource tree. This behavior is gated by a new > >> kernel option CONFIG_SOFT_RESERVED_MANAGED. > >> > > > > I'm missing a bit of context here. > > > > Why can't we flag these regions in the existing iomem tree, where they can be fixed up (even after boot?)? > > > > Especially, what about deferred driver loading after boot? Why is that not a concern or why can we reliably handle everything "during boot" ? > > That's a good question and one I should have addressed. > > The goal is to prevent the dax driver from creating dax devices for soft reserve > resources prior to the soft reserve resources being updated for any intersecting > cxl regions. Not an export. Can you explain a little more here? What is the problem if we only flag the resources as "soft reserved" in the iomem tree without creating a separate tree, and process the "soft reserved" resources only when needed? Fan > > During boot the dax hmem driver walks the iomem tree to save off a copy of all > soft reserve resources. The dax driver then later walks this copy to create > dax devices for the soft reserve regions. This occurs before the cxl drivers > load, create cxl regions, and update any intersecting soft reserve resources. > > To prevent this the soft reserves are set aside on a separate list during boot > so that they can be updated (if needed) and later added to the iomem resource tree. > The dax driver is then notified of any soft reserves added to the iomem tree > so that it may consume them. > > Hopefully that answers your question. I'll include this in the next version. > > -Nathan > > > > >> As part of this update two new interfaces are added for management of > >> the SOFT RESERVED resources. The release_srmem_region_adjustable() > >> routine allows for removing pieces of SOFT RESERVED resources. The > >> the merge_srmem_resources() allows drivers to merge any remaining SOFT > >> RESERVED resources into the iomem resource tree once updatea are complete. > >> > >> Signed-off-by: Nathan Fontenot <nathan.fontenot@xxxxxxx> > > >
