linux-kernel - Re: [PATCH v3 6/7] KVM: SVM: Add support to initialize SEV/SNP functionality in KVM

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Message-ID: <8ae7718c-2321-4f3a-b5b7-7fb029d150cf@amd.com>
Date: Tue, 7 Jan 2025 12:34:01 -0600
From: "Kalra, Ashish" <ashish.kalra@....com>
To: Tom Lendacky <thomas.lendacky@....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, davem@...emloft.net
Cc: michael.roth@....com, dionnaglaze@...gle.com, kvm@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
 linux-coco@...ts.linux.dev
Subject: Re: [PATCH v3 6/7] KVM: SVM: Add support to initialize SEV/SNP
 functionality in KVM



On 1/7/2025 10:42 AM, Tom Lendacky wrote:
> On 1/3/25 14:01, Ashish Kalra wrote:
>> From: Ashish Kalra <ashish.kalra@....com>
>>
>> Remove platform initialization of SEV/SNP from PSP driver probe time and
> 
> Actually, you're not removing it, yet...
> 
>> move it to KVM module load time so that KVM can do SEV/SNP platform
>> initialization explicitly if it actually wants to use SEV/SNP
>> functionality.
>>
>> With this patch, KVM will explicitly call into the PSP driver at load time
>> to initialize SEV/SNP by default but this behavior can be altered with KVM
>> module parameters to not do SEV/SNP platform initialization at module load
>> time if required. Additionally SEV/SNP platform shutdown is invoked during
>> KVM module unload time.
>>
>> Signed-off-by: Ashish Kalra <ashish.kalra@....com>
>> ---
>>  arch/x86/kvm/svm/sev.c | 15 ++++++++++++++-
>>  1 file changed, 14 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
>> index 943bd074a5d3..0dc8294582c6 100644
>> --- a/arch/x86/kvm/svm/sev.c
>> +++ b/arch/x86/kvm/svm/sev.c
>> @@ -444,7 +444,6 @@ static int __sev_guest_init(struct kvm *kvm, struct kvm_sev_cmd *argp,
>>  	if (ret)
>>  		goto e_no_asid;
>>  
>> -	init_args.probe = false;
>>  	ret = sev_platform_init(&init_args);
>>  	if (ret)
>>  		goto e_free;
>> @@ -2953,6 +2952,7 @@ 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};
> 
> Will this cause issues if KVM is built-in and INIT_EX is being used
> (init_ex_path ccp parameter)? The probe parameter is used for
> initialization done before the filesystem is available.
> 

Yes, this will cause issues if KVM is builtin and INIT_EX is being used,
but my question is how will INIT_EX be used when we move SEV INIT
to KVM ?

If we continue to use the probe field here and also continue to support
psp_init_on_probe module parameter for CCP, how will SEV INIT_EX be
invoked ? 

How is SEV INIT_EX invoked in PSP driver currently if psp_init_on_probe
parameter is set to false ?

The KVM path to invoke sev_platform_init() when a SEV VM is being launched 
cannot be used because QEMU checks for SEV to be initialized before
invoking this code path to launch the guest.

Thanks,
Ashish

> Thanks,
> Tom
> 
>>  	bool sev_snp_supported = false;
>>  	bool sev_es_supported = false;
>>  	bool sev_supported = false;
>> @@ -3069,6 +3069,16 @@ 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.
>> +	 */
>> +	sev_platform_init(&init_args);
>>  }
>>  
>>  void sev_hardware_unsetup(void)
>> @@ -3084,6 +3094,9 @@ 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)