linux-kernel - Re: [PATCH v2] x86/smpboot: Remove 486-isms from the modern AP boot path

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Message-ID: <b15b8cf2-a579-10ec-06b1-fb674295c993@citrix.com>
Date:   Wed, 1 Apr 2020 15:47:19 +0100
From:   Andrew Cooper <andrew.cooper3@...rix.com>
To:     Brian Gerst <brgerst@...il.com>
CC:     LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        Jan Kiszka <jan.kiszka@...mens.com>,
        James Morris <jmorris@...ei.org>,
        David Howells <dhowells@...hat.com>,
        Matthew Garrett <mjg59@...gle.com>,
        Josh Boyer <jwboyer@...hat.com>,
        Steve Wahl <steve.wahl@....com>,
        Mike Travis <mike.travis@....com>,
        Dimitri Sivanich <dimitri.sivanich@....com>,
        "Arnd Bergmann" <arnd@...db.de>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Giovanni Gherdovich <ggherdovich@...e.cz>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Len Brown <len.brown@...el.com>,
        Kees Cook <keescook@...omium.org>,
        Martin Molnar <martin.molnar.programming@...il.com>,
        Pingfan Liu <kernelfans@...il.com>,
        <jailhouse-dev@...glegroups.com>
Subject: Re: [PATCH v2] x86/smpboot: Remove 486-isms from the modern AP boot
 path

On 01/04/2020 15:38, Brian Gerst wrote:
>>>>>>> You removed x86_platform.legacy.warm_reset in the original patch, but
>>>>>>> that is missing in V2.
>>>>>> Second hunk?  Or are you referring to something different?
>>>>> Removing the warm_reset field from struct x86_legacy_features.
>>>> Ok, but that is still present as the 2nd hunk of the patch.
>>> My apologies, Gmail was hiding that section of the patch because it
>>> was a reply to the original patch.  For future reference, add the
>>> version number to the title when resubmitting a patch (ie. [PATCH
>>> v2]).
>> Erm... is Gmail hiding that too?
>>
>> Lore thinks it is there:
>> https://lore.kernel.org/lkml/CAMzpN2g0LS5anGc7CXco4pgBHhGzc8hw+shMOg8WEWGsx+BHpg@mail.gmail.com/
> Ugh, yes.  I thought it was the title that Gmail threaded on, but it
> must be the In-Reply-To: header.  Sorry for the confusion.
>
> That said, I think the v1 patch is probably the better way to go (but
> adjusting the comments to include early Pentium-era systems without
> integrated APICs).

Yes - I'm afraid I'm showing my age here, being the same vintage as the 486.

I'll happily rephrase as suggested.

> Then the decision to drop support for external
> APICs could be a separate patch.

I have no vested interest.

This was a fix from Xen that I tried to upstream (if you can really call
it that, seeing as the common point in history was the Linux 2.4 days),
given the rather rude UEFI behaviour.

Ultimately, this will be down to the maintainers for which approach to take.

~Andrew