linux-kernel - Re: [patch 37/53] x86/cpu: Detect real BSP on crash kernels

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Date: Wed, 10 Jan 2024 15:19:58 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: "Zhang, Rui" <rui.zhang@...el.com>, "linux-kernel@...r.kernel.org"
 <linux-kernel@...r.kernel.org>
Cc: "jgross@...e.com" <jgross@...e.com>, "x86@...nel.org" <x86@...nel.org>,
 "arjan@...ux.intel.com" <arjan@...ux.intel.com>, "kprateek.nayak@....com"
 <kprateek.nayak@....com>, "Tang, Feng" <feng.tang@...el.com>,
 "kan.liang@...ux.intel.com" <kan.liang@...ux.intel.com>,
 "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>, "paulmck@...nel.org" <paulmck@...nel.org>,
 "Mehta, Sohil" <sohil.mehta@...el.com>, "andy@...radead.org"
 <andy@...radead.org>
Subject: Re: [patch 37/53] x86/cpu: Detect real BSP on crash kernels

On Tue, Jan 09 2024 at 01:54, Zhang, Rui wrote:
> On Mon, 2024-01-08 at 17:13 +0100, Thomas Gleixner wrote:
>> > > Unfortunately this causes a regression on Intel Meteorlake
>> > > platform,
>> > > where the BSP APIC ID is NOT the lowest numbered APIC ID
>> > > (instead,
>> > > CPU12, the first Ecore CPU, has APIC ID 0).
>> > 
>> > Bah. Let me think about that.
>> 
>> In which order are the APICs/CPUs enumerated by ACPI?
>
>
> This is the order in MADT,
> $ cat apic.dsl  | grep x2Apic
> [030h 0048   4]          Processor x2Apic ID : 00000010
> [040h 0064   4]          Processor x2Apic ID : 00000011
> [050h 0080   4]          Processor x2Apic ID : 00000018
> [060h 0096   4]          Processor x2Apic ID : 00000019
> [070h 0112   4]          Processor x2Apic ID : 00000020
> [080h 0128   4]          Processor x2Apic ID : 00000021
> [090h 0144   4]          Processor x2Apic ID : 00000028
> [0A0h 0160   4]          Processor x2Apic ID : 00000029
> [0B0h 0176   4]          Processor x2Apic ID : 00000030
> [0C0h 0192   4]          Processor x2Apic ID : 00000031
> [0D0h 0208   4]          Processor x2Apic ID : 00000038
> [0E0h 0224   4]          Processor x2Apic ID : 00000039
> [0F0h 0240   4]          Processor x2Apic ID : 00000000
> [100h 0256   4]          Processor x2Apic ID : 00000002
> [110h 0272   4]          Processor x2Apic ID : 00000004
> [120h 0288   4]          Processor x2Apic ID : 00000006
> [130h 0304   4]          Processor x2Apic ID : 00000008
> [140h 0320   4]          Processor x2Apic ID : 0000000A
> [150h 0336   4]          Processor x2Apic ID : 0000000C
> [160h 0352   4]          Processor x2Apic ID : 0000000E
> [170h 0368   4]          Processor x2Apic ID : 00000040
> [180h 0384   4]          Processor x2Apic ID : 00000042
>
> and this is the order in Linux (from CPU0 to CPUN)
>       x2APIC ID of logical processor = 0x20 (32)
>       x2APIC ID of logical processor = 0x10 (16)
>       x2APIC ID of logical processor = 0x11 (17)
>       x2APIC ID of logical processor = 0x18 (24)
>       x2APIC ID of logical processor = 0x19 (25)
>       x2APIC ID of logical processor = 0x21 (33)
>       x2APIC ID of logical processor = 0x28 (40)
>       x2APIC ID of logical processor = 0x29 (41)
>       x2APIC ID of logical processor = 0x30 (48)
>       x2APIC ID of logical processor = 0x31 (49)
>       x2APIC ID of logical processor = 0x38 (56)
>       x2APIC ID of logical processor = 0x39 (57)
>       x2APIC ID of logical processor = 0x0 (0)
>       x2APIC ID of logical processor = 0x2 (2)
>       x2APIC ID of logical processor = 0x4 (4)
>       x2APIC ID of logical processor = 0x6 (6)
>       x2APIC ID of logical processor = 0x8 (8)
>       x2APIC ID of logical processor = 0xa (10)
>       x2APIC ID of logical processor = 0xc (12)
>       x2APIC ID of logical processor = 0xe (14)
>       x2APIC ID of logical processor = 0x40 (64)
>       x2APIC ID of logical processor = 0x42 (66)

What a mess...