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

Tom Lendacky
2025-01-08T17:22:44Z

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@amd.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@amd.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)
>