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

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Message-ID: <ee9d2956-fa55-4c83-b17d-055df7e1150c@amd.com>
Date: Wed, 8 Jan 2025 18:27:42 -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 1/8/2025 11:22 AM, Tom Lendacky wrote:
> 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, i will make sure that we continue to support both the probe
field and psp_init_on_probe module parameter for CCP modules as part of v4.

>>
>>> 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)
>>