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

On 5/8/25 17:52, Ashish Kalra wrote:

From: Ashish Kalra ashish.kalra@amd.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@google.com Signed-off-by: Sean Christopherson seanjc@google.com Co-developed-by: Pratik R. Sampat prsampat@amd.com Signed-off-by: Pratik R. Sampat prsampat@amd.com Signed-off-by: Ashish Kalra ashish.kalra@amd.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) +{

• struct sev_user_data_snp_status *status;
• struct sev_data_snp_addr buf;
• bool initialized = false;
• void *data;

No need for 'data', just allocate directly to 'status', no?

• int error;

if (!sev_snp_supported) return false;

No need to issue the command if it doesn't matter.

• data = snp_alloc_firmware_page(GFP_KERNEL_ACCOUNT | __GFP_ZERO);

GFP_KERNEL instead of GFP_KERNEL_ACCOUNT ?

• if (!data)

• return initialized;
  

return false;

I like explicit values in these conditions, but that's just me.

• buf.address = __psp_pa(data);
• if (sev_do_cmd(SEV_CMD_SNP_PLATFORM_STATUS, &buf, &error))

You should issue an error message here or not pass in error (I would prefer the former).

• goto out;
  

• status = (struct sev_user_data_snp_status *)data;
• if (status->state)

• initialized = true;
  

initialized = !!status->state; ?

+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();
  

With changes above, then you can just do:

sev_snp_supported = sev_is_snp_initialized()

Thanks, Tom

• }
• 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;

• 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)