linux-kernel - Re: [PATCH v2] KVM: SEV: Disable SEV-SNP support on initialization failure

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Message-ID: <ed6cf930-bb1d-d082-a1c7-f5699ec46565@amd.com>
Date: Mon, 12 May 2025 16:55:27 -0500
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, shuah@...nel.org, prsampat@....com
Cc: pgonda@...gle.com, nikunj@....com, pankaj.gupta@....com,
 michael.roth@....com, sraithal@....com, linux-kernel@...r.kernel.org,
 x86@...nel.org, kvm@...r.kernel.org, linux-kselftest@...r.kernel.org,
 linux-coco@...ts.linux.dev
Subject: Re: [PATCH v2] KVM: SEV: Disable SEV-SNP support on initialization
 failure

On 5/12/25 16:04, Ashish Kalra wrote:
> From: Ashish Kalra <ashish.kalra@....com>
> 
> During platform init, SNP initialization may fail for several reasons,
> such as firmware command failures and incompatible versions. However,
> the KVM capability may continue to advertise support for it.
> 
> The platform may have SNP enabled but if SNP_INIT fails then SNP is
> not supported by KVM.
> 
> During KVM module initialization query the SNP platform status to obtain
> the SNP initialization state and use it as an additional condition to
> determine support for SEV-SNP.
> 
> Co-developed-by: Sean Christopherson <seanjc@...gle.com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> Co-developed-by: Pratik R. Sampat <prsampat@....com>
> Signed-off-by: Pratik R. Sampat <prsampat@....com>
> Signed-off-by: Ashish Kalra <ashish.kalra@....com>

One comment below, otherwise:

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

> ---
>  arch/x86/kvm/svm/sev.c | 44 +++++++++++++++++++++++++++++++++---------
>  1 file changed, 35 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index dea9480b9ff6..f7d343ab9acd 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -2935,6 +2935,33 @@ void __init sev_set_cpu_caps(void)
>  	}
>  }
>  
> +static bool is_sev_snp_initialized(void)
> +{
> +	struct sev_user_data_snp_status *status;
> +	struct sev_data_snp_addr buf;
> +	bool initialized = false;
> +	int error, ret;
> +
> +	status = snp_alloc_firmware_page(GFP_KERNEL | __GFP_ZERO);
> +	if (!status)
> +		return false;
> +
> +	buf.address = __psp_pa(status);
> +	ret = sev_do_cmd(SEV_CMD_SNP_PLATFORM_STATUS, &buf, &error);

You'll want to initialize error to 0 or you'll get a possible use of
uninitialized variable.

Thanks,
Tom

> +	if (ret) {
> +		pr_err("SEV: SNP_PLATFORM_STATUS failed ret=%d, fw_error=%d (%#x)\n",
> +		       ret, error, error);
> +		goto out;
> +	}
> +
> +	initialized = !!status->state;
> +
> +out:
> +	snp_free_firmware_page(status);
> +
> +	return initialized;
> +}
> +
>  void __init sev_hardware_setup(void)
>  {
>  	unsigned int eax, ebx, ecx, edx, sev_asid_count, sev_es_asid_count;
> @@ -3039,6 +3066,14 @@ void __init sev_hardware_setup(void)
>  	sev_snp_supported = sev_snp_enabled && cc_platform_has(CC_ATTR_HOST_SEV_SNP);
>  
>  out:
> +	if (sev_enabled) {
> +		init_args.probe = true;
> +		if (sev_platform_init(&init_args))
> +			sev_supported = sev_es_supported = sev_snp_supported = false;
> +		else if (sev_snp_supported)
> +			sev_snp_supported = is_sev_snp_initialized();
> +	}
> +
>  	if (boot_cpu_has(X86_FEATURE_SEV))
>  		pr_info("SEV %s (ASIDs %u - %u)\n",
>  			sev_supported ? min_sev_asid <= max_sev_asid ? "enabled" :
> @@ -3065,15 +3100,6 @@ 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;
> -
> -	/*
> -	 * Do both SNP and SEV initialization at KVM module load.
> -	 */
> -	init_args.probe = true;
> -	sev_platform_init(&init_args);
>  }
>  
>  void sev_hardware_unsetup(void)