Re: [PATCH v16 00/17] KVM RISC-V Support

[Paolo Bonzini]

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.

Paolo

> Regards,
> Anup
>
> On Tue, Apr 27, 2021 at 11:13 AM Paul Walmsley <paul.walmsley@xxxxxxxxxx> wrote:
> > On Fri, 9 Apr 2021, Palmer Dabbelt wrote:
> >
> > > On Wed, 31 Mar 2021 02:21:58 PDT (-0700), pbonzini@xxxxxxxxxx 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