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Subject: Re: [PATCH v6 07/11] x86/smpboot: Disable parallel boot for AMD CPUs
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From:   Kim Phillips <kim.phillips@amd.com>
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On 2/6/23 11:58 AM, Kim Phillips wrote:
> 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.

The Ryzen 3000 also successfully boots those two branches now.

Thanks,

Kim