Re: [PATCH v6 06/11] x86/smpboot: Support parallel startup of secondary CPUs

[David Woodhouse <dwmw2@infradead.org>]

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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. 

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