linux-kernel - Re: [PATCH v6 9/9] KVM: selftests: Add a basic SEV-SNP smoke test

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Message-ID: <e3136d20-977a-4e2d-ad7b-c04be1dca1db@amd.com>
Date: Fri, 14 Feb 2025 12:14:19 -0600
From: Pratik Rajesh Sampat <prsampat@....com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org, kvm@...r.kernel.org,
 linux-crypto@...r.kernel.org, linux-kselftest@...r.kernel.org,
 pbonzini@...hat.com, thomas.lendacky@....com, tglx@...utronix.de,
 mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
 shuah@...nel.org, pgonda@...gle.com, ashish.kalra@....com, nikunj@....com,
 pankaj.gupta@....com, michael.roth@....com, sraithal@....com
Subject: Re: [PATCH v6 9/9] KVM: selftests: Add a basic SEV-SNP smoke test



On 2/11/25 8:31 PM, Sean Christopherson wrote:
> On Mon, Feb 03, 2025, Pratik R. Sampat wrote:
>> @@ -217,5 +244,20 @@ int main(int argc, char *argv[])
>>  		}
>>  	}
>>  
>> +	if (kvm_cpu_has(X86_FEATURE_SEV_SNP)) {
>> +		uint64_t snp_policy = snp_default_policy();
>> +
>> +		test_snp(snp_policy);
>> +		/* Test minimum firmware level */
>> +		test_snp(snp_policy | SNP_FW_VER_MAJOR(SNP_MIN_API_MAJOR) |
>> +			SNP_FW_VER_MINOR(SNP_MIN_API_MINOR));
> 
> Ah, this is where the firmware policy stuff is used.  Refresh me, can userspace
> request _any_ major/minor as the min, and expect failure if the version isn't
> supported?  If so, the test should iterate over the major/minor combinations that
> are guaranteed to fail.  And if userspace can query the supported minor/major,
> the test should iterate over all the happy versions too. 
> 

Yes, any policy greater than the min policy (defined in sev-dev.c)
should be supported. The sad path tests were intended to be added in the
upcoming negative test patch series so that we could have the proper
infrastructure to handle and report failures.

> Unless there's nothing interesting to test, I would move the major/minor stuff to
> a separate patch.

Would you rather prefer I do the happy tests here (something like -
min_policy and min_policy + 1?) and defer the failure tests for the
next patchset? Or, I can remove policy testing from here entirely and
introduce it only when the sad path testing infrastructure is ready, so
that we can test this completely at once?

> 
>> +
>> +		test_snp_shutdown(snp_policy);
>> +
>> +		if (kvm_has_cap(KVM_CAP_XCRS) &&
>> +		    (xgetbv(0) & kvm_cpu_supported_xcr0() & xf_mask) == xf_mask)
>> +			test_sync_vmsa_snp(snp_policy);
> 
> This is all copy+paste from SEV-ES tests, minus SEV_POLICY_NO_DBG.  There's gotta
> be a way to dedup this code.
> 
> Something like this?
> 
> static void needs_a_better_name(uint32_t type, uint64_t policy)
> {
> 	const u64 xf_mask = XFEATURE_MASK_X87_AVX;
> 
> 	test_sev(guest_sev_code, policy | SEV_POLICY_NO_DBG);
> 	test_sev(guest_sev_code, policy);
> 
> 	if (type == KVM_X86_SEV_VM)
> 		return;
> 
> 	test_sev_shutdown(policy);
> 
> 	if (kvm_has_cap(KVM_CAP_XCRS) &&
> 	    (xgetbv(0) & kvm_cpu_supported_xcr0() & xf_mask) == xf_mask) {
> 		test_sync_vmsa(policy);
> 		test_sync_vmsa(policy | SEV_POLICY_NO_DBG);
> 	}
> }
> 
> int main(int argc, char *argv[])
> {
> 	TEST_REQUIRE(kvm_cpu_has(X86_FEATURE_SEV));
> 
> 	needs_a_better_name(KVM_X86_SEV_VM, 0);
> 
> 	if (kvm_cpu_has(X86_FEATURE_SEV_ES))
> 		needs_a_better_name(KVM_X86_SEV_ES_VM, 0);
> 
> 	if (kvm_cpu_has(X86_FEATURE_SEV_SNP))
> 		needs_a_better_name(KVM_X86_SEV_SNP_VM, 0);
> 
> 	return 0;
> }

Sure, I can definitely clean this up so that we have less duplication of
code all around for this test.

Thanks again!
Pratik