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

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Message-ID: <8adf7f48-dab0-cbed-d920-e3b74d8411cf@amd.com>
Date: Wed, 8 Jan 2025 11:22:39 -0600
From: Tom Lendacky <thomas.lendacky@....com>
To: "Kalra, Ashish" <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, 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 1/7/25 12:34, Kalra, Ashish wrote:
> 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.

Qemu only requires that for an SEV-ES guest. I was able to use the
init_ex_path=/root/... and psp_init_on_probe=0 to successfully delay SEV
INIT_EX and launch an SEV guest.

Thanks,
Tom

> 
> 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)
>