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

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Date:   Mon, 31 Jul 2023 15:27:14 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>
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 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?