Le 24/08/2017 à 20:47, Benjamin Herrenschmidt a écrit :
On Thu, 2017-08-24 at 18:40 +0200, Frederic Barrat wrote:
The decrementing part is giving me troubles, and I think it makes sense:
if I decrement the counter when detaching the context from the capi
card, then the next TLBIs for the memory context may be back to local.
Yes, you need to flush the CAPI TLB first.
So when the process exits, the NPU wouldn't get the associated TLBIs,
which spells trouble the next time the same memory context ID is reused.
I believe this the cause of the problem I'm seeing. As soon as I keep
the TLBIs global, even after I detach from the capi adapter, everything
is fine.
Does it sound right?
So to keep the checks minimal in mm_is_thread_local(), to just checking
the active_cpus count, I'm thinking of introducing a "copro enabled" bit
on the context, so that we can increment active_cpus only once. And
never decrement it.
You can decrement if you flush. Don't you have MMIOs to do directed
flushes ?
That's for the nMMU. Last I heard, we don't have MMIOs to flush anything
on the nMMU.
Side note: for the PSL, we do have MMIOs to flush, but they were
perceived as useful only for debug and we don't rely on them, precisely
because the nMMU would fall out of sync, so we have to rely on broadcast.
Fred
