Date:   Fri, 3 Feb 2023 18:17:04 +0000
From:   Sean Christopherson <seanjc@google.com>
To:     Usama Arif <usama.arif@bytedance.com>
Cc:     dwmw2@infradead.org, tglx@linutronix.de, arjan@linux.intel.com,
        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,
        pmenzel@molgen.mpg.de, fam.zheng@bytedance.com,
        punit.agrawal@bytedance.com, simon.evans@bytedance.com,
        liangma@liangbit.com
Subject: Re: [PATCH v6 06/11] x86/smpboot: Support parallel startup of
 secondary CPUs
Message-ID: <Y91PoIfc2jdRv0WG@google.com>
References: <20230202215625.3248306-1-usama.arif@bytedance.com>
 <20230202215625.3248306-7-usama.arif@bytedance.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20230202215625.3248306-7-usama.arif@bytedance.com>
Precedence: bulk

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();
>  }