Date:   Mon, 13 Mar 2023 11:38:58 -0700
From:   Oliver Upton <oliver.upton@linux.dev>
To:     Sean Christopherson <seanjc@google.com>
Cc:     Bagas Sanjaya <bagasdotme@gmail.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Sagi Shahar <sagis@google.com>,
        Erdem Aktas <erdemaktas@google.com>,
        Peter Shier <pshier@google.com>,
        Anish Ghulati <aghulati@google.com>,
        James Houghton <jthoughton@google.com>,
        Anish Moorthy <amoorthy@google.com>,
        Ben Gardon <bgardon@google.com>,
        David Matlack <dmatlack@google.com>,
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        Axel Rasmussen <axelrasmussen@google.com>,
        Aaron Lewis <aaronlewis@google.com>,
        Ashish Kalra <ashish.kalra@amd.com>,
        Babu Moger <babu.moger@amd.com>, Chao Gao <chao.gao@intel.com>,
        Chao Peng <chao.p.peng@linux.intel.com>,
        Chenyi Qiang <chenyi.qiang@intel.com>,
        David Woodhouse <dwmw@amazon.co.uk>,
        Emanuele Giuseppe Esposito <eesposit@redhat.com>,
        Gavin Shan <gshan@redhat.com>,
        Guang Zeng <guang.zeng@intel.com>,
        Hou Wenlong <houwenlong.hwl@antgroup.com>,
        Jiaxi Chen <jiaxi.chen@linux.intel.com>,
        Jim Mattson <jmattson@google.com>,
        Jing Liu <jing2.liu@intel.com>,
        Junaid Shahid <junaids@google.com>,
        Kai Huang <kai.huang@intel.com>,
        Leonardo Bras <leobras@redhat.com>,
        Like Xu <like.xu.linux@gmail.com>,
        Li RongQing <lirongqing@baidu.com>,
        "Maciej S . Szmigiero" <maciej.szmigiero@oracle.com>,
        Maxim Levitsky <mlevitsk@redhat.com>,
        Michael Roth <michael.roth@amd.com>,
        Michal Luczaj <mhal@rbox.co>,
        Mingwei Zhang <mizhang@google.com>,
        Nikunj A Dadhania <nikunj@amd.com>,
        Paul Durrant <pdurrant@amazon.com>,
        Peng Hao <flyingpenghao@gmail.com>,
        Peter Gonda <pgonda@google.com>, Peter Xu <peterx@redhat.com>,
        Robert Hoo <robert.hu@linux.intel.com>,
        Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Vipin Sharma <vipinsh@google.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Wei Wang <wei.w.wang@intel.com>,
        Xiaoyao Li <xiaoyao.li@intel.com>,
        Yu Zhang <yu.c.zhang@linux.intel.com>,
        Zhenzhong Duan <zhenzhong.duan@intel.com>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 2/2] Documentation/process: Add a maintainer handbook
 for KVM x86
Message-ID: <ZA9twqv5XQMmgXWb@thinky-boi>
References: <20230309010336.519123-1-seanjc@google.com>
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On Mon, Mar 13, 2023 at 11:20:45AM -0700, Sean Christopherson wrote:
> On Mon, Mar 13, 2023, Oliver Upton wrote:
> > On Thu, Mar 09, 2023 at 09:25:54AM -0800, Sean Christopherson wrote:
> > > On Thu, Mar 09, 2023, Oliver Upton wrote:
> > > > On Thu, Mar 09, 2023 at 09:37:45AM +0700, Bagas Sanjaya wrote:
> > > > > On Wed, Mar 08, 2023 at 05:03:36PM -0800, Sean Christopherson wrote:
> > > > > > +As a general guideline, use ``kvm-x86/next`` even if a patch/series touches
> > > > > > +multiple architectures, i.e. isn't strictly scoped to x86.  Using any of the
> > > > > > +branches from the main KVM tree is usually a less good option as they likely
> > > > > > +won't have many, if any, changes for the next release, i.e. using the main KVM
> > > > > > +tree as a base is more likely to yield conflicts.  And if there are non-trivial
> > > > > > +conflicts with multiple architectures, coordination between maintainers will be
> > > > > > +required no matter what base is used.  Note, this is far from a hard rule, i.e.
> > > > > > +use a different base for multi-arch series if that makes the most sense.
> > > > 
> > > > I don't think this is the best way to coordinate with other architectures.
> > > > Regardless of whether you intended this to be prescriptive, I'm worried most
> > > > folks will follow along and just base patches on kvm-x86/next anyway.
> > > 
> > > Probably, but for the target audience (KVM x86 contributors), that's likely the
> > > least awful base 99% of the time.
> > 
> > Sorry, I follow this reasoning at all.
> > 
> > If folks are aiming to make a multi-arch contribution then the architecture
> > they regularly contribute to has absolutely zero relevance on the series
> > itself.
> 
> There's disconnect between what my brain is thinking and what I wrote.
> 
> The intent of the "use kvm-x86/next" guideline is aimed to address series that
> are almost entirely x86 specific, and only superficially touch common KVM and/or
> other architectures.  In my experience, the vast, vast majority of "multi-arch"
> contributions from x86 fall into this category, i.e. aren't truly multi-arch in
> nature.
> 
> If I replace the above paragraph with this, does that address (or at least mitigate
> to an acceptable level) your concerns?  Inevitably there will still be series that
> are wrongly based on kvm-x86, but I am more than happy to do the policing.  I
> obviously can't guarantee that I will be the first to run afoul of a "bad" series,
> but I do think I can be quick enough to avoid shifting the burden to other
> maintainers.  And if I'm wrong on either front, you get to say "told you so" and
> make me submit a patch of shame ;-)
> 
>   The only exception to using ``kvm-x86/next`` as the base is if a patch/series
>   is a multi-arch series, i.e. has non-trivial modifications to common KVM code
>   and/or has more than superficial changes to other architectures's code.  Multi-

nit: Maybe 'to another architecture's code', since English is an annoying
language :)

>   arch patch/series should instead be based on a common, stable point in KVM's
>   history, e.g. the release candidate upon which ``kvm-x86 next`` is based.  If
>   you're unsure whether a patch/series is truly multi-arch, err on the side of
>   caution and treat it as multi-arch, i.e. use a common base.

LGTM, and sorry for whining without getting across the net effect I was hoping
for in the language.

> > > > > That means patches that primarily kvm ARM changes should be based on
> > > > > kvm-x86/next, right?
> > > > 
> > > > No, don't do that.
> > > 
> > > +<infinity symbol>
> > > 
> > > This doc is specifically for KVM x86.
> > 
> > You've also made some suggestions about cross-arch development that do not fit
> > the development model of other architectures. I have no desire to nitpick
> > about the x86 process but want the multiarch language to actually set folks up
> > for success working outside of the KVM/x86 tree.
> 
> Ah, I see where y'all are coming from.  Yeah, I didn't intend for that type of
> blanket rule, e.g. my comment about this being specifically for KVM x86 was
> intended to clarify that this doc should NOT be used to determine how to handle
> non-x86 code.

My biggest worry was that whether intentional or not, folks will probably take
what you've written out of context. Not as though I could completely blame the
developer in that case, as we have no documented process for arm64 at the
moment.

--
Thanks,
Oliver