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

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Message-ID: <e71453cd-3d7d-4c7b-b763-3e47236ac955@amd.com>
Date: Fri, 9 May 2025 12:52:05 -0500
From: "Kalra, Ashish" <ashish.kalra@....com>
To: "Paluri, PavanKumar" <papaluri@....com>, seanjc@...gle.com,
 pbonzini@...hat.com, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
 dave.hansen@...ux.intel.com, thomas.lendacky@....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,
 "Paluri, PavanKumar (Pavan Kumar)" <pavankumar.paluri@....com>
Subject: Re: [PATCH] KVM: SEV: Disable SEV-SNP support on initialization
 failure


On 5/9/2025 12:01 PM, Paluri, PavanKumar wrote:
> 
> 
> On 5/8/2025 5:52 PM, 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>
>> ---
>>  arch/x86/kvm/svm/sev.c | 43 +++++++++++++++++++++++++++++++++---------
>>  1 file changed, 34 insertions(+), 9 deletions(-)
>>
>> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
>> index ada53f04158c..a6abdb26f877 100644
>> --- a/arch/x86/kvm/svm/sev.c
>> +++ b/arch/x86/kvm/svm/sev.c
>> @@ -2934,6 +2934,32 @@ void __init sev_set_cpu_caps(void)
>>  	}
>>  }
>>  
>> +static bool sev_is_snp_initialized(void)
> 
> s/sev_is_snp_initialized/is_sev_snp_initalized looks better.
>

Actually the convention is sev_is_xx(). 
 
>> +{
>> +	struct sev_user_data_snp_status *status;
>> +	struct sev_data_snp_addr buf;
>> +	bool initialized = false;
>> +	void *data;
>> +	int error;
>> +
>> +	data = snp_alloc_firmware_page(GFP_KERNEL_ACCOUNT | __GFP_ZERO);
>> +	if (!data)
>> +		return initialized;
>> +
>> +	buf.address = __psp_pa(data);
>> +	if (sev_do_cmd(SEV_CMD_SNP_PLATFORM_STATUS, &buf, &error))
>> +		goto out;
>> +
>> +	status = (struct sev_user_data_snp_status *)data;
>> +	if (status->state)
>> +		initialized = true;
>> +
>> +out:
>> +	snp_free_firmware_page(data);
>> +
>> +	return initialized;
>> +}
>> +
>>  void __init sev_hardware_setup(void)
>>  {
>>  	unsigned int eax, ebx, ecx, edx, sev_asid_count, sev_es_asid_count;
>> @@ -3038,6 +3064,14 @@ 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
>> +			sev_snp_supported &= sev_is_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" :
>> @@ -3064,15 +3098,6 @@ 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;
> 
> On what kernel version is this patch based on? I do not see the below
> diff in 6.15-rc5.
>

This is based on linux-next.

Thanks,
Ashish
 
> Thanks,
> Pavan
>> -
>> -	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)
>