Message-ID: <fb3e75fa-1a6f-0570-218f-ba9133fb72c6@bytedance.com>
Date:   Thu, 2 Feb 2023 22:50:40 +0000
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Subject: Re: [External] Re: [PATCH v6 06/11] x86/smpboot: Support parallel
 startup of secondary CPUs
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To:     David Woodhouse <dwmw2@infradead.org>, tglx@linutronix.de,
        arjan@linux.intel.com
Cc:     mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com,
        hpa@zytor.com, x86@kernel.org, pbonzini@redhat.com,
        paulmck@kernel.org, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org, rcu@vger.kernel.org, mimoja@mimoja.de,
        hewenliang4@huawei.com, thomas.lendacky@amd.com, seanjc@google.com,
        pmenzel@molgen.mpg.de, fam.zheng@bytedance.com,
        punit.agrawal@bytedance.com, simon.evans@bytedance.com,
        liangma@liangbit.com
References: <20230202215625.3248306-1-usama.arif@bytedance.com>
 <20230202215625.3248306-7-usama.arif@bytedance.com>
 <dac090d2a61137b9e2fecd6cb3bfb4d5a9656fb6.camel@infradead.org>
From:   Usama Arif <usama.arif@bytedance.com>
In-Reply-To: <dac090d2a61137b9e2fecd6cb3bfb4d5a9656fb6.camel@infradead.org>
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On 02/02/2023 22:30, David Woodhouse wrote:
> On Thu, 2023-02-02 at 21:56 +0000, Usama Arif wrote:
>> @@ -1515,6 +1530,17 @@ void __init native_smp_prepare_cpus(unsigned int max_cpus)
>>   
>>          speculative_store_bypass_ht_init();
>>   
>> +       /*
>> +        * We can do 64-bit AP bringup in parallel if the CPU reports its
>> +        * APIC ID in CPUID leaf 0x0B. Otherwise it's too hard. And not
>> +        * for SEV-ES guests because they can't use CPUID that early.
>> +        * Also, some AMD CPUs crash when doing parallel cpu bringup, disable
>> +        * it for all AMD CPUs to be on the safe side.
>> +        */
>> +       if (IS_ENABLED(CONFIG_X86_32) || boot_cpu_data.cpuid_level < 0x0B ||
>> +           cc_platform_has(CC_ATTR_GUEST_STATE_ENCRYPT))
>> +               do_parallel_bringup = false;
>> +
>>          snp_set_wakeup_secondary_cpu();
>>   }
> 
> Oops, I thought I'd removed those two lines about AMD in the comment
> when I removed the actual code that did so. Turns out we remove those
> lines again in the *next* patch instead.

Ah, sorry about that, should have caught it while reviewing before 
posting. To think of it, it might be better to squash this and next AMD 
disabling patch, if anyone testing on AMD ever happens to check out at 
this specific patch, their machine might not boot :). Will repost only 
after getting the OK for the rest of the patches along with addressing 
any other comments that come up.

Thanks,
Usama