linux-kernel - Re: [RFC 3/5] selftests: KVM: SEV IOCTL test

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Message-ID: <37fe0c7f-a99d-4c16-86d5-24b45ce2bbb4@amd.com>
Date: Tue, 13 Aug 2024 10:23:24 -0500
From: "Pratik R. Sampat" <pratikrajesh.sampat@....com>
To: Sean Christopherson <seanjc@...gle.com>
CC: Tom Lendacky <thomas.lendacky@....com>, <kvm@...r.kernel.org>,
	<shuah@...nel.org>, <michael.roth@....com>, <pbonzini@...hat.com>,
	<pgonda@...gle.com>, <linux-kselftest@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [RFC 3/5] selftests: KVM: SEV IOCTL test



On 8/9/2024 10:45 AM, Sean Christopherson wrote:
> On Thu, Jul 11, 2024, Pratik Rajesh Sampat wrote:
>>>> +static void sev_guest_status_assert(struct kvm_vm *vm, uint32_t type)
>>>> +{
>>>> +	struct kvm_sev_guest_status status;
>>>> +	bool cond;
>>>> +	int ret;
>>>> +
>>>> +	ret = __vm_sev_ioctl(vm, KVM_SEV_GUEST_STATUS, &status);
>>>> +	cond = type == KVM_X86_SEV_VM ? !ret : ret;
>>>> +	TEST_ASSERT(cond,
>>>> +		    "KVM_SEV_GUEST_STATUS should fail, invalid VM Type.");
>>>> +}
>>>> +
>>>> +static void test_sev_launch(void *guest_code, uint32_t type, uint64_t policy)
>>>> +{
>>>> +	struct kvm_vcpu *vcpu;
>>>> +	struct kvm_vm *vm;
>>>> +	struct ucall uc;
>>>> +	bool cond;
>>>> +	int ret;
>>>> +
>>>
>>> Maybe a block comment here indicating what you're actually doing would
>>> be good, because I'm a bit confused.
>>>
>>> A policy value of 0 is valid for SEV, so you expect each call to
>>> succeed, right? And, actually, for SEV-ES the launch start will succeed,
>>> too, but the launch update will fail because LAUNCH_UPDATE_VMSA is not
>>> valid for SEV, but then the launch measure should succeed. Is that
>>> right? What about the other calls?
>>>
>>
>> Sure, I can do that.
>> Yes for SEV, the policy value of 0 succeeds for everything except when
>> we try to run and we see a KVM_EXIT_IO.
>>
>> For SEV-ES, with the policy value of 0 - we don't see launch_start
>> succeed. It fails with EIO in this case. Post that all the calls for
>> SEV-ES also fail subsequent to that. I guess the core idea behind this
>> test is to ensure that once the first bad case of launch_start fails, we
>> should see a cascading list of failures.
>>
>>>> +	vm = vm_sev_create_with_one_vcpu(type, guest_code, &vcpu);
>>>> +	ret = sev_vm_launch_start(vm, 0);
>>>> +	cond = type == KVM_X86_SEV_VM ? !ret : ret;
>>>> +	TEST_ASSERT(cond,
> 
> Don't bury the result in a local boolean.  It's confusing, and _worse_ for debug
> as it makes it impossible to see what actually failed (the assert message will
> simply print "cond", which is useless).
> 

Ack, I will make sure all the other occurrences of using similar boolean
are also removed and the conditions themselves are passed into the assert.

> 
>>>> +		    "KVM_SEV_LAUNCH_START should fail, invalid policy.");
> 
> This is a blatant lie, because the KVM_X86_SEV_VM case apparently expects success.
> Similar to Tom's comments about explaing what this code is doing, these assert
> messages need to explain what the actually expected result it, provide a hint as
> to _why_ that result is expected, and print the result.  As is, this will be
> unnecessarily difficult to debug if/when it fails.

Right. I'll make the error messages more reflective of what they are as
well as have an explanation to why we expect this behavior.

Thanks!
- Pratik