On Wed, 2025-01-29 at 09:47 -0400, Jason Gunthorpe wrote: > 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.. Just a comment on the performance concern here. This can be crafted in a way that only if the driver provides a callback, there is a (small) hit. If there is no callback at that point, we're looking at a migration to ram. If there is a callback it's typically followed by an address computation and page-table setup. Compared to those, the callback performance impact is probably unmeasureable. /Thomas
