linux-kernel - Re: [patch V3 27/40] x86/cpu: Provide a sane leaf 0xb/0x1f parser

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Date:   Sun, 13 Aug 2023 17:04:37 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Zhang, Rui" <rui.zhang@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:     "Gross, Jurgen" <jgross@...e.com>,
        "mikelley@...rosoft.com" <mikelley@...rosoft.com>,
        "arjan@...ux.intel.com" <arjan@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "thomas.lendacky@....com" <thomas.lendacky@....com>,
        "ray.huang@....com" <ray.huang@....com>,
        "andrew.cooper3@...rix.com" <andrew.cooper3@...rix.com>,
        "Sivanich, Dimitri" <dimitri.sivanich@....com>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>
Subject: Re: [patch V3 27/40] x86/cpu: Provide a sane leaf 0xb/0x1f parser

On Sat, Aug 12 2023 at 22:04, Thomas Gleixner wrote:
> On Sat, Aug 12 2023 at 08:21, Rui Zhang wrote:
>> With this, we can guarantee that all the available topology information
>> are always valid, even when running on future platforms.
>
> I know that it can be made work, but is it worth the extra effort? I
> don't think so.

So I thought more about it. For intermediate levels, i.e. something
which is squeezed between two existing levels, this works by some
definition of works.

I.e. the example where we have UBER_TILE between TILE and DIE, then we'd
set and propagate the UBER_TILE entry into the DIE slot and then
overwrite it again, if there is a DIE entry too.

Where it becomes interesting is when the unknown level is past DIEGRP,
e.g. DIEGRP_CONGLOMORATE then we'd need to overwrite the DIEGRP level,
right?

It can be done, but I don't know whether it buys us much for the purely
theoretical case of new levels added.

Thanks,

        tglx