linux-kernel - Re: [PATCH v4 6/7] KVM: SVM: Add support to initialize SEV/SNP functionality in KVM

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Message-ID: <22ac00dd-cd36-82af-0a72-86dc34c08e5a@amd.com>
Date: Thu, 20 Feb 2025 13:57:36 -0600
From: Tom Lendacky <thomas.lendacky@....com>
To: Ashish Kalra <Ashish.Kalra@....com>, seanjc@...gle.com,
 pbonzini@...hat.com, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
 dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
 john.allen@....com, herbert@...dor.apana.org.au
Cc: michael.roth@....com, dionnaglaze@...gle.com, nikunj@....com,
 ardb@...nel.org, kevinloughlin@...gle.com, Neeraj.Upadhyay@....com,
 aik@....com, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-crypto@...r.kernel.org, linux-coco@...ts.linux.dev
Subject: Re: [PATCH v4 6/7] KVM: SVM: Add support to initialize SEV/SNP
 functionality in KVM

On 2/19/25 14:54, Ashish Kalra wrote:
> From: Ashish Kalra <ashish.kalra@....com>
> 
> Move platform initialization of SEV/SNP from PSP driver probe time to

s/PSP/CCP/

> KVM module load time so that KVM can do SEV/SNP platform initialization
> explicitly if it actually wants to use SEV/SNP functionality.
> 
> Add support for KVM to explicitly call into the PSP driver at load time

s/PSP/CCP/

> to initialize SEV/SNP by default but this behavior can be altered with KVM

s/by default but this/. If required, this/

> module parameters to not do SEV/SNP platform initialization at module load
> time if required. Additionally SEV/SNP platform shutdown is invoked during

s/if required//
s/Additionally/Additionally, a corresponding/

> KVM module unload time.

Some commit message comments and a minor comment below, otherwise:

Reviewed-by: Tom Lendacky <thomas.lendacky@....com>

> 
> Suggested-by: Sean Christopherson <seanjc@...gle.com>
> Signed-off-by: Ashish Kalra <ashish.kalra@....com>
> ---
>  arch/x86/kvm/svm/sev.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 74525651770a..213d4c15a9da 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -2933,6 +2933,7 @@ void __init sev_set_cpu_caps(void)
>  void __init sev_hardware_setup(void)
>  {
>  	unsigned int eax, ebx, ecx, edx, sev_asid_count, sev_es_asid_count;
> +	struct sev_platform_init_args init_args = {0};
>  	bool sev_snp_supported = false;
>  	bool sev_es_supported = false;
>  	bool sev_supported = false;
> @@ -3059,6 +3060,17 @@ void __init sev_hardware_setup(void)
>  	sev_supported_vmsa_features = 0;
>  	if (sev_es_debug_swap_enabled)
>  		sev_supported_vmsa_features |= SVM_SEV_FEAT_DEBUG_SWAP;
> +
> +	if (!sev_enabled)
> +		return;
> +
> +	/*
> +	 * NOTE: Always do SNP INIT regardless of sev_snp_supported
> +	 * as SNP INIT has to be done to launch legacy SEV/SEV-ES
> +	 * VMs in case SNP is enabled system-wide.
> +	 */

But won't this also do an SEV init as long as init_on_probe is true? And
isn't this true for even non-SEV VMs? You have to pause all VMs before
performing SNP INIT. In which case I don't see the point of this
comment. I think you really just want to say:

	/*
	 * Always perform SEV initialization at setup time to avoid
	 * complications with performing SEV initialization later
	 * (such as suspending active guests, etc.).
	 */

Not that that is much better... but it's more accurate.

Thanks,
Tom

> +	init_args.probe = true;
> +	sev_platform_init(&init_args);
>  }
>  
>  void sev_hardware_unsetup(void)
> @@ -3074,6 +3086,9 @@ void sev_hardware_unsetup(void)
>  
>  	misc_cg_set_capacity(MISC_CG_RES_SEV, 0);
>  	misc_cg_set_capacity(MISC_CG_RES_SEV_ES, 0);
> +
> +	/* Do SEV and SNP Shutdown */
> +	sev_platform_shutdown();
>  }
>  
>  int sev_cpu_init(struct svm_cpu_data *sd)