Re: [PATCH RFC 11/14] arm64: Move the ASID allocator code in a separate file

[Palmer Dabbelt]

On Thu, 12 Sep 2019 07:02:56 PDT (-0700), will@xxxxxxxxxx wrote:
> On Sun, Sep 08, 2019 at 07:52:55AM +0800, Guo Ren wrote:
> > On Mon, Jun 24, 2019 at 6:40 PM Will Deacon <will@xxxxxxxxxx> wrote:
> > > > I'll keep my system use the same ASID for SMP + IOMMU :P
> > >
> > > You will want a separate allocator for that:
> > >
> > > https://lkml.kernel.org/r/20190610184714.6786-2-jean-philippe.brucker@xxxxxxx
> >
> > Yes, it is hard to maintain ASID between IOMMU and CPUMMU or different
> > system, because it's difficult to synchronize the IO_ASID when the CPU
> > ASID is rollover.
> > But we could still use hardware broadcast TLB invalidation instruction
> > to uniformly manage the ASID and IO_ASID, or OTHER_ASID in our IOMMU.
>
> That's probably a bad idea, because you'll likely stall execution on the
> CPU until the IOTLB has completed invalidation. In the case of ATS, I think
> an endpoint ATC is permitted to take over a minute to respond. In reality, I
> suspect the worst you'll ever see would be in the msec range, but that's
> still an unacceptable period of time to hold a CPU.
>
> > Welcome to join our disscusion:
> > "Introduce an implementation of IOMMU in linux-riscv"
> > 9 Sep 2019, 10:45 Jade-room-I&II (Corinthia Hotel Lisbon) RISC-V MC
>
> I attended this session, but it unfortunately raised many more questions
> than it answered.

Ya, we're a long way from figuring this out.