Message-ID: <abb08aaf96cbee2ae16852b10a75bf9e865813da.camel@infradead.org>
Subject: Re: [EXTERNAL][PATCH v6 04/11] x86/smpboot: Reference count on
 smpboot_setup_warm_reset_vector()
From:   David Woodhouse <dwmw2@infradead.org>
To:     Thomas Gleixner <tglx@linutronix.de>,
        "usama.arif@bytedance.com" <usama.arif@bytedance.com>,
        "arjan@linux.intel.com" <arjan@linux.intel.com>
Cc:     "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
        "thomas.lendacky@amd.com" <thomas.lendacky@amd.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "seanjc@google.com" <seanjc@google.com>,
        "mingo@redhat.com" <mingo@redhat.com>,
        "fam.zheng@bytedance.com" <fam.zheng@bytedance.com>,
        "pbonzini@redhat.com" <pbonzini@redhat.com>,
        "liangma@liangbit.com" <liangma@liangbit.com>,
        "pmenzel@molgen.mpg.de" <pmenzel@molgen.mpg.de>,
        "mimoja@mimoja.de" <mimoja@mimoja.de>,
        "hewenliang4@huawei.com" <hewenliang4@huawei.com>,
        "hpa@zytor.com" <hpa@zytor.com>,
        "punit.agrawal@bytedance.com" <punit.agrawal@bytedance.com>,
        "simon.evans@bytedance.com" <simon.evans@bytedance.com>,
        "bp@alien8.de" <bp@alien8.de>,
        "paulmck@kernel.org" <paulmck@kernel.org>,
        "rcu@vger.kernel.org" <rcu@vger.kernel.org>,
        "x86@kernel.org" <x86@kernel.org>
Date:   Tue, 07 Feb 2023 19:48:06 +0000
In-Reply-To: <87sffhv8to.ffs@tglx>
References: <20230202215625.3248306-1-usama.arif@bytedance.com>
         <20230202215625.3248306-5-usama.arif@bytedance.com> <871qn2xsmf.ffs@tglx>
         <57195f701f6d1d70ec440c9a28cbee4cfb81dc41.camel@amazon.co.uk>
         <87sffhv8to.ffs@tglx>
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On Tue, 2023-02-07 at 15:39 +0100, Thomas Gleixner wrote:
> David!
>=20
> On Tue, Feb 07 2023 at 09:49, David Woodhouse wrote:
>=20
> Can you please fix your mail client to _NOT_ send multipart/mixed mails?
> Despite the CC list being insanely large, your replies are dropped by
> vger and missing in the archives.
>=20

That's not the client; that's the stupid mail system doing it in
transit. Sorry, I'd already filed a ticket about that idiocy last week
when I noticed they'd started adding HTML parts to a previously sane
mail. But obviously they haven't managed to fix it yet.

The correct thing to do in the meantime is use a non-broken mail
account, and I just forgot this morning until half way through the
thread, when you'll note the coffee kicked in and I switched.


> > On Tue, 2023-02-07 at 00:48 +0100, Thomas Gleixner wrote:
> > > On Thu, Feb 02 2023 at 21:56, Usama Arif wrote:
> > > > From: David Woodhouse <dwmw@amazon.co.uk>
> > > >=20
> > > > If we want to do parallel CPU bringup, we're going to need to set t=
his up
> > > > and leave it until all CPUs are done. Might as well use the RTC spi=
nlock
> > > > to protect the refcount, as we need to take it anyway.
> > >=20
> > > https://www.kernel.org/doc/html/latest/process/maintainer-tip.html#ch=
angelog
> > >=20
> > > Aside of the 'We' this does not explain anything at all.
> >=20
> > Er, doesn't it?
> >=20
> > We refcount the warm reset vector because when we do parallel bringup,
> > we'll want to set it up once and then put it back to normal (for cold
> > reset) once all the CPUs are up.
> >=20
> > I can rework the phrasing; I'm aware that the whole nonsense about
> > pronouns and the imperative mood has grown legs in the last couple of
> > years since I originally wrote it =E2=80=94 but is there anything actua=
lly
> > missing?
>=20
> We can settle the imperative mood debate over a beer at the next
> conference, but stuff which goes through tip is required to follow those
> rules. No exception for you :)
>=20
> Vs. the content: This changelog lacks context. Changelogs have to be
> self contained and self explanatory. Assuming that they are
> understandable due to the context of the patch series is just wrong. I
> fundamentally hate it when I have to dig out the context when I stare at
> the changelog of a commit.
>=20
> So something like this:
>=20
> =C2=A0=C2=A0 The warm reset vector on X86 is setup through the RTC (CMOS)=
 clock
> =C2=A0=C2=A0 for each CPU bringup operation and cleared after the CPU cam=
e online.
>=20
> =C2=A0=C2=A0 Parallel bringup of multiple CPUs requires that the warm res=
et vector
> =C2=A0=C2=A0 is valid until all CPUs came online.
>=20
> =C2=A0=C2=A0 To prepare for that add refcounting for the reset vector and=
 protect
> =C2=A0=C2=A0 it with the rtc_lock which has to be taken for the setup ope=
ration
> =C2=A0=C2=A0 anyway.
>=20
> gives the full context and is simply factual, no?

Ack.

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