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From:   Kim Phillips <kim.phillips@amd.com>
Subject: Re: [PATCH v6 07/11] x86/smpboot: Disable parallel boot for AMD CPUs
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On 2/4/23 9:40 AM, David Woodhouse wrote:
> On Fri, 2023-02-03 at 13:48 -0600, Kim Phillips wrote:
>> If I:
>>
>>    - take dwmw2's parallel-6.2-rc6 branch (commit 459d1c46dbd1)
>>    - remove the set_cpu_bug(c, X86_BUG_NO_PARALLEL_BRINGUP) line from amd.c
>>
>> Then:
>>
>>    - a Ryzen 3000 (Picasso A1/Zen+) notebook I have access to fails to boot.
>>    - Zen 2,3,4-based servers boot fine
>>    - a Zen1-based server doesn't boot.
> 
> I've changed it to use CPUID 0xb only if we're actually in x2apic mode,
> which Boris tells me won't be the case on Zen1 because that doesn't
> support X2APIC.
> 
> When we're not in x2apic mode, we can use CPUID 0x1 because the 8 bits
> of APIC ID we find there are perfectly sufficient.
> 
> New tree in the same place as before, commit ce7e2d1e046a for the
> parallel-6.2-rc6-part1 tag and 17bbd12ee03 for parallel-6.2-rc6.

Thanks, Zen 1 through 4 based servers all boot both those two tree
commits successfully.

I'll try that Ryzen again later.

Kim