Nicholas Piggin <npiggin@xxxxxxxxx> writes: > Excerpts from Linus Torvalds's message of July 29, 2020 5:02 am: >> On Tue, Jul 28, 2020 at 3:53 AM Nicholas Piggin <npiggin@xxxxxxxxx> wrote: >>> >>> The quirk is a problem with coprocessor where it's supposed to >>> invalidate the translation after a fault but it doesn't, so we can get a >>> read-only TLB stuck after something else does a RO->RW upgrade on the >>> TLB. Something like that IIRC. Coprocessors have their own MMU which >>> lives in the nest not the core, so you need a global TLB flush to >>> invalidate that thing. >> >> So I assumed, but it does seem confused. >> >> Why? Because if there are stale translations on the co-processor, >> there's no guarantee that one of the CPU's will have them and take a >> fault. >> >> So I'm not seeing why a core CPU doing spurious TLB invalidation would >> follow from "stale TLB in the Nest". > > If the nest MMU access faults, it sends an interrupt to the CPU and > the driver tries to handle the page fault for it (I think that's how > it works). Yeah AFAIK. I think they all end up calling copro_handle_mm_fault(). Except for NX/vas, where the model is a fault just causes the request to be dropped and sent back to userspace to fix things up. cheers
