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

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Message-ID: <Y91PoIfc2jdRv0WG@google.com>
Date:   Fri, 3 Feb 2023 18:17:04 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Usama Arif <usama.arif@...edance.com>
Cc:     dwmw2@...radead.org, tglx@...utronix.de, arjan@...ux.intel.com,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        hpa@...or.com, x86@...nel.org, pbonzini@...hat.com,
        paulmck@...nel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, rcu@...r.kernel.org, mimoja@...oja.de,
        hewenliang4@...wei.com, thomas.lendacky@....com,
        pmenzel@...gen.mpg.de, fam.zheng@...edance.com,
        punit.agrawal@...edance.com, simon.evans@...edance.com,
        liangma@...ngbit.com
Subject: Re: [PATCH v6 06/11] x86/smpboot: Support parallel startup of
 secondary CPUs

On Thu, Feb 02, 2023, 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))

Obviously not your fault, but CC_ATTR_GUEST_STATE_ENCRYPT is a terrible name.
TDX guest state is also encrypted, but TDX doesn't return true CC_ATTR_GUEST_STATE_ENCRYPT.
I.e. this looks wrong, but is correct, because CC_ATTR_GUEST_STATE_ENCRYPT really
just means "SEV-ES guest".

> +		do_parallel_bringup = false;
> +
>  	snp_set_wakeup_secondary_cpu();
>  }