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

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Date:   Sun, 15 Sep 2019 05:03:38 +0000
From:   Anup Patel <Anup.Patel@....com>
To:     Palmer Dabbelt <palmer@...ive.com>,
        "will@...nel.org" <will@...nel.org>
CC:     "guoren@...nel.org" <guoren@...nel.org>,
        Will Deacon <will.deacon@....com>,
        "julien.thierry@....com" <julien.thierry@....com>,
        "aou@...s.berkeley.edu" <aou@...s.berkeley.edu>,
        "james.morse@....com" <james.morse@....com>,
        Arnd Bergmann <arnd@...db.de>,
        "suzuki.poulose@....com" <suzuki.poulose@....com>,
        "marc.zyngier@....com" <marc.zyngier@....com>,
        "catalin.marinas@....com" <catalin.marinas@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "rppt@...ux.ibm.com" <rppt@...ux.ibm.com>,
        Christoph Hellwig <hch@...radead.org>,
        Atish Patra <Atish.Patra@....com>,
        "julien.grall@....com" <julien.grall@....com>,
        "gary@...yguo.net" <gary@...yguo.net>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        "christoffer.dall@....com" <christoffer.dall@....com>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "kvmarm@...ts.cs.columbia.edu" <kvmarm@...ts.cs.columbia.edu>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>
Subject: RE: [PATCH RFC 11/14] arm64: Move the ASID allocator code in a
 separate file



> -----Original Message-----
> From: linux-kernel-owner@...r.kernel.org <linux-kernel-
> owner@...r.kernel.org> On Behalf Of Palmer Dabbelt
> Sent: Saturday, September 14, 2019 7:31 PM
> To: will@...nel.org
> Cc: guoren@...nel.org; 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@....com; catalin.marinas@....com; Anup Patel
> <Anup.Patel@....com>; linux-kernel@...r.kernel.org;
> rppt@...ux.ibm.com; Christoph Hellwig <hch@...radead.org>; Atish Patra
> <Atish.Patra@....com>; julien.grall@....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
> 
> On Thu, 12 Sep 2019 07:02:56 PDT (-0700), 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.bruck
> >> > er@....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.
> >
> >> 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.

For everyone's reference, here is our first attempt at RISC-V ASID allocator:
http://archive.lwn.net:8080/linux-kernel/20190329045111.14040-1-anup.patel@....com/T/#u

Regards,
Anup