[PATCH v16 00/17] KVM RISC-V Support
anup at brainfault.org
Wed Apr 28 08:07:25 BST 2021
On Tue, Apr 27, 2021 at 12:34 PM Paolo Bonzini <pbonzini at redhat.com> wrote:
> On 27/04/21 08:01, Anup Patel wrote:
> > Hi Paolo,
> > Looks like it will take more time for KVM RISC-V to be merged under arch/riscv.
> > Let's go ahead with your suggestion of having KVM RISC-V under drivers/staging
> > so that development is not blocked.
> > I will send-out v18 series which will add KVM RISC-V under the staging
> > directory.
> > Should we target Linux-5.14 ?
> Yes, 5.14 is reasonable. You'll have to adjust the MMU notifiers for
> the new API introduced in 5.13.
Sure, I will rebase on the new API introduced in 5.13
> > Regards,
> > Anup
> > On Tue, Apr 27, 2021 at 11:13 AM Paul Walmsley <paul.walmsley at sifive.com> wrote:
> >> On Fri, 9 Apr 2021, Palmer Dabbelt wrote:
> >>> On Wed, 31 Mar 2021 02:21:58 PDT (-0700), pbonzini at redhat.com wrote:
> >>>> Palmer, are you okay with merging RISC-V KVM? Or should we place it in
> >>>> drivers/staging/riscv/kvm?
> >>> I'm certainly ready to drop my objections to merging the code based on
> >>> it targeting a draft extension, but at a bare minimum I want to get a
> >>> new policy in place that everyone can agree to for merging code. I've
> >>> tried to draft up a new policy a handful of times this week, but I'm not
> >>> really quite sure how to go about this: ultimately trying to build
> >>> stable interfaces around an unstable ISA is just a losing battle. I've
> >>> got a bunch of stuff going on right now, but I'll try to find some time
> >>> to actually sit down and finish one.
> >>> I know it might seem odd to complain about how slowly things are going
> >>> and then throw up another roadblock, but I really do think this is a
> >>> very important thing to get right. I'm just not sure how we're going to
> >>> get anywhere with RISC-V without someone providing stability, so I want
> >>> to make sure that whatever we do here can be done reliably. If we don't
> >>> I'm worried the vendors are just going to go off and do their own
> >>> software stacks, which will make getting everyone back on the same page
> >>> very difficult.
> >> I sympathize with Paolo, Anup, and others also. Especially Anup, who has
> >> been updating and carrying the hypervisor patches for a long time now.
> >> And also Greentime, who has been carrying the V extension patches. The
> >> RISC-V hypervisor specification, like several other RISC-V draft
> >> specifications, is taking longer to transition to the officially "frozen"
> >> stage than almost anyone in the RISC-V community would like.
> >> Since we share this frustration, the next questions are:
> >> - What are the root causes of the problem?
> >> - What's the right forum to address the root causes?
> >> To me, the root causes of the problems described in this thread aren't
> >> with the arch/riscv kernel maintenance guidelines, but rather with the
> >> RISC-V specification process itself. And the right forum to address
> >> issues with the RISC-V specification process is with RISC-V International
> >> itself: the mailing lists, the participants, and the board of directors.
> >> Part of the challenge -- not simply with RISC-V, but with the Linux kernel
> >> or any other community -- is to ensure that incentives (and disincentives)
> >> are aligned with the appropriately responsible parts of the community.
> >> And when it comes to specification development, the right focus to align
> >> those incentives and disincentives is on RISC-V International.
> >> The arch/riscv patch acceptance guidelines are simply intended to ensure
> >> that the definition of what is and isn't RISC-V remains clear and
> >> unambiguous. Even though the guidelines can result in short-term pain,
> >> the intention is to promote long-term stability and sustainable
> >> maintainability - particularly since the specifications get baked into
> >> hardware. We've observed that attempting to chase draft specifications
> >> can cause significant churn: for example, the history of the RISC-V vector
> >> specification illustrates how a draft extension can undergo major,
> >> unexpected revisions throughout its journey towards ratification. One of
> >> our responsibilities as kernel developers is to minimize that churn - not
> >> simply for our own sanity, or for the usability of RISC-V, but to ensure
> >> that we remain members in good standing of the broader kernel community.
> >> Those of us who were around for the ARM32 and ARM SoC kernel accelerando
> >> absorbed strong lessons in maintainability, and I doubt anyone here is
> >> interested in re-learning those the hard way.
> >> RVI states that the association is open to community participation. The
> >> organizations that have joined RVI, I believe, have a strong stake in the
> >> health of the RISC-V ecosystem, just as the folks have here in this
> >> discussion. If the goal really is to get quality specifications out the
> >> door faster, then let's focus the energy towards building consensus
> >> towards improving the process at RISC-V International. If that's
> >> possible, the benefits won't only accrue to Linux developers, but to the
> >> entire RISC-V hardware and software development community at large. If
> >> nothing else, it will be an interesting test of whether RISC-V
> >> International can take action to address these concerns and balance them
> >> with those of other stakeholders in the process.
> >> - Paul
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