linux-kernel - RE: [PATCH v6 7/8] x86/hyperv: Add smp support for SEV-SNP guest

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Message-ID: <SA1PR21MB1335F165EF353A24E4CCF6F0BF15A@SA1PR21MB1335.namprd21.prod.outlook.com>
Date:   Wed, 16 Aug 2023 21:42:52 +0000
From:   Dexuan Cui <decui@...rosoft.com>
To:     Tianyu Lan <ltykernel@...il.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>,
        "daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
        "arnd@...db.de" <arnd@...db.de>,
        "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
CC:     Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        vkuznets <vkuznets@...hat.com>,
        "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
Subject: RE: [PATCH v6 7/8] x86/hyperv: Add smp support for SEV-SNP guest

> From: Tianyu Lan <ltykernel@...il.com>
> Sent: Wednesday, August 16, 2023 8:59 AM
> [...]
> --- a/arch/x86/kernel/cpu/mshyperv.c
> +++ b/arch/x86/kernel/cpu/mshyperv.c
> @@ -295,6 +295,16 @@ static void __init hv_smp_prepare_cpus(unsigned
> int max_cpus)
> 
>  	native_smp_prepare_cpus(max_cpus);
>  [...]
> +	if (hv_isolation_type_en_snp())
> +		apic->wakeup_secondary_cpu_64 = hv_snp_boot_ap;
> +
> +	if (!hv_root_partition)
> +		return;

Can the above be changed to:

	if (hv_isolation_type_en_snp()) {
		apic->wakeup_secondary_cpu_64 = hv_snp_boot_ap;
		return;
	}

(please also see the below)

> +
>  #ifdef CONFIG_X86_64
>  	for_each_present_cpu(i) {
>  		if (i == 0)
> @@ -502,8 +512,7 @@ static void __init ms_hyperv_init_platform(void)
> 
>  # ifdef CONFIG_SMP
>  	smp_ops.smp_prepare_boot_cpu = hv_smp_prepare_boot_cpu;
> -	if (hv_root_partition)
> -		smp_ops.smp_prepare_cpus = hv_smp_prepare_cpus;
> +	smp_ops.smp_prepare_cpus = hv_smp_prepare_cpus;

IMO it's better if we don't unconditionally change smp_ops.smp_prepare_cpus.

How about this:
	if (hv_root_partition || hv_isolation_type_en_snp())
		smp_ops.smp_prepare_cpus = hv_smp_prepare_cpus;