linux-kernel - Re: [patch v2 21/38] x86/cpu: Provide cpu_init/parse

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Date:   Mon, 31 Jul 2023 17:38:21 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     "Michael Kelley (LINUX)" <mikelley@...rosoft.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        Dick Kennedy <dick.kennedy@...adcom.com>,
        James Smart <james.smart@...adcom.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        Guenter Roeck <linux@...ck-us.net>,
        "linux-hwmon@...r.kernel.org" <linux-hwmon@...r.kernel.org>,
        Jean Delvare <jdelvare@...e.com>,
        Huang Rui <ray.huang@....com>, Juergen Gross <jgross@...e.com>,
        Steve Wahl <steve.wahl@....com>,
        Mike Travis <mike.travis@....com>,
        Dimitri Sivanich <dimitri.sivanich@....com>,
        Russ Anderson <russ.anderson@....com>
Subject: Re: [patch v2 21/38] x86/cpu: Provide cpu_init/parse_topology()

On Mon, Jul 31 2023 at 15:27, Peter Zijlstra wrote:
> On Mon, Jul 31, 2023 at 02:34:39PM +0200, Thomas Gleixner wrote:
>> This collides massively with the other work I'm doing, which uses the
>> MADT provided information to actually evaluate various topology related
>> things upfront and later during bringup. Thats badly needed because lots
>> of todays infrastructure is based on heuristics and guesswork.
>> 
>> But it seems I wasted a month on reworking all of this just to be
>> stopped cold in the tracks by completely undocumented and unnecessary
>> hyper-v abuse.
>> 
>> So if Hyper-V insists on abusing the initial APIC ID as read from CPUID
>> for topology information related to L3, then hyper-v should override the
>> cache topology mechanism and not impose this insanity on the basic
>> topology evaluation infrastructure.
>
> So I'm very tempted to suggest you continue with the topology rewrite
> and let Hyper-V keep the pieces. They're very clearly violating the SDM.
>
> Thing as they stand are untenable, the whole topology thing as it exists
> today is an untenable shitshow.
>
> Michael, is there anything you can do early (as in MADT parse early) to
> fix up the APIC-IDs?

I don't think so.

Michael, can you please provide me a table of:

   APICID (real/MADT)		APICID (CPUID)

from one of the tinker VMs please?

Thanks,

        tglx