On Wed, Jan 29, 2025 at 02:38:58PM +0100, Simona Vetter wrote: > > The pgmap->owner doesn't *have* to fixed, certainly during early boot before > > you hand out any page references it can be changed. I wouldn't be > > surprised if this is useful to some requirements to build up the > > private interconnect topology? > > The trouble I'm seeing is device probe and the fundemantal issue that you > never know when you're done. And so if we entirely rely on pgmap->owner to > figure out the driver private interconnect topology, that's going to be > messy. That's why I'm also leaning towards both comparing owners and > having an additional check whether the interconnect is actually there or > not yet. Hoenstely, I'd rather invest more effort into being able to update owner for those special corner cases than to slow down the fast path in hmm_range_fault.. The notion is that owner should represent a contiguous region of connectivity. IMHO you can always create this, but I suppose there could be corner cases where you need to split/merge owners. But again, this isn't set in stone, if someone has a better way to match the private interconnects without going to driver callbacks then try that too. I think driver callbacks inside hmm_range_fault should be the last resort.. > You can fake that by doing these checks after hmm_range_fault returned, > and if you get a bunch of unsuitable pages, toss it back to > hmm_range_fault asking for an unconditional migration to system memory for > those. But that's kinda not great and I think goes at least against the > spirit of how you want to handle pci p2p in step 2 below? Right, hmm_range_fault should return pages that can be used and you should not call it twice. Jason
