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Date: Wed, 1 Apr 2020 10:38:51 -0400 From: Brian Gerst <brgerst@...il.com> To: Andrew Cooper <andrew.cooper3@...rix.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 Wed, Apr 1, 2020 at 8:14 AM Andrew Cooper <andrew.cooper3@...rix.com> wrote: > > On 01/04/2020 12:39, Brian Gerst wrote: > > On Wed, Apr 1, 2020 at 5:22 AM Andrew Cooper <andrew.cooper3@...rix.com> wrote: > >> On 31/03/2020 23:53, Brian Gerst wrote: > >>> On Tue, Mar 31, 2020 at 6:44 PM Andrew Cooper <andrew.cooper3@...rix.com> wrote: > >>>> On 31/03/2020 23:23, Brian Gerst wrote: > >>>>> On Tue, Mar 31, 2020 at 1:59 PM Andrew Cooper <andrew.cooper3@...rix.com> wrote: > >>>>>> Linux has an implementation of the Universal Start-up Algorithm (MP spec, > >>>>>> Appendix B.4, Application Processor Startup), which includes unconditionally > >>>>>> writing to the Bios Data Area and CMOS registers. > >>>>>> > >>>>>> The warm reset vector is only necessary in the non-integrated Local APIC case. > >>>>>> UV and Jailhouse already have an opt-out for this behaviour, but blindly using > >>>>>> the BDA and CMOS on a UEFI or other reduced hardware system isn't clever. > >>>>>> > >>>>>> We could make this conditional on the integrated-ness of the Local APIC, but > >>>>>> 486-era SMP isn't supported. Drop the logic completely, tidying up the includ > >>>>>> list and header files as appropriate. > >>>>>> > >>>>> 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). Then the decision to drop support for external APICs could be a separate patch. -- Brian Gerst
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