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

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Date:   Thu, 12 Sep 2019 15:59:43 +0100
From:   Guo Ren <guoren@...nel.org>
To:     Will Deacon <will@...nel.org>
Cc:     Will Deacon <will.deacon@....com>, julien.thierry@....com,
        aou@...s.berkeley.edu, james.morse@....com,
        Arnd Bergmann <arnd@...db.de>, suzuki.poulose@....com,
        Marc Zyngier <marc.zyngier@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Anup Patel <anup.Patel@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Christoph Hellwig <hch@...radead.org>,
        Atish Patra <Atish.Patra@....com>,
        Julien Grall <julien.grall@....com>,
        Palmer Dabbelt <palmer@...ive.com>, gary@...yguo.net,
        Paul Walmsley <paul.walmsley@...ive.com>,
        christoffer.dall@....com, linux-riscv@...ts.infradead.org,
        kvmarm@...ts.cs.columbia.edu, linux-arm-kernel@...ts.infradead.org,
        iommu@...ts.linux-foundation.org
Subject: Re: [PATCH RFC 11/14] arm64: Move the ASID allocator code in a
 separate file

Thx Will for reply.

On Thu, Sep 12, 2019 at 3:03 PM Will Deacon <will@...nel.org> 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@...nel.org> 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@arm.com
> >
> > 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.
Just as I've said in the session that IOTLB invalidate delay is
another topic, My main proposal is to introduce stage1.pgd and
stage2.pgd as address space identifiers between different TLB systems
based on vmid, asid. My last part of sildes will show you how to
translate stage1/2.pgd to as/vmid in PCI ATS system and the method
could work with SMMU-v3 and intel Vt-d. (It's regret for me there is
no time to show you the whole slides.)

In our light IOMMU implementation, there's no IOTLB invalidate delay
problem. Becasue IOMMU is very close to CPU MMU and interconnect's
delay is the same with SMP CPUs MMU (no PCI, VM supported).

To solve the problem, we could define a async mode in sfence.vma.b to
slove the problem and finished with per_cpu_irq/exception.

-- 
Best Regards
 Guo Ren

ML: https://lore.kernel.org/linux-csky/