linux-kernel - Re: [RFC 2/5] selftests: KVM: Decouple SEV ioctls from asserts

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Message-ID: <Zrt7bRGQJ1C9XZGy@google.com>
Date: Tue, 13 Aug 2024 08:27:41 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: "Pratik R. Sampat" <pratikrajesh.sampat@....com>
Cc: kvm@...r.kernel.org, shuah@...nel.org, thomas.lendacky@....com, 
	michael.roth@....com, pbonzini@...hat.com, pgonda@...gle.com, 
	linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC 2/5] selftests: KVM: Decouple SEV ioctls from asserts

On Tue, Aug 13, 2024, Pratik R. Sampat wrote:
> On 8/9/2024 10:40 AM, Sean Christopherson wrote:
> > On Wed, Jul 10, 2024, Pratik R. Sampat wrote:
> >> @@ -98,7 +100,7 @@ static inline void sev_register_encrypted_memory(struct kvm_vm *vm,
> >>  	vm_ioctl(vm, KVM_MEMORY_ENCRYPT_REG_REGION, &range);
> >>  }
> >>  
> >> -static inline void snp_launch_update_data(struct kvm_vm *vm, vm_paddr_t gpa,
> >> +static inline int snp_launch_update_data(struct kvm_vm *vm, vm_paddr_t gpa,
> >>  					   uint64_t size, uint8_t type)
> >>  {
> >>  	struct kvm_sev_snp_launch_update update_data = {
> >> @@ -108,10 +110,10 @@ static inline void snp_launch_update_data(struct kvm_vm *vm, vm_paddr_t gpa,
> >>  		.type = type,
> >>  	};
> >>  
> >> -	vm_sev_ioctl(vm, KVM_SEV_SNP_LAUNCH_UPDATE, &update_data);
> >> +	return __vm_sev_ioctl(vm, KVM_SEV_SNP_LAUNCH_UPDATE, &update_data);
> > 
> > Don't introduce APIs and then immediately rewrite all of the users.  If you want
> > to rework similar APIs, do the rework, then add the new APIs.  Doing things in
> > this order adds a pile of pointless churn.
> > 
> > But that's a moot point, because it's far easier to just add __snp_launch_update_data().
> > And if you look through other APIs in kvm_util.h, you'll see that the strong
> > preference is to let vm_ioctl(), or in this case vm_sev_ioctl(), do the heavy
> > lifting.  Yeah, it requires copy+pasting marshalling parameters into the struct,
> > but that's relatively uninteresting code, _and_ piggybacking the "good" version
> > means you can't do things like pass in a garbage virtual address (because the
> > "good" version always guarantees a good virtual address).
> 
> I am a little confused by this.
> 
> Are you suggesting that I leave the original functions intact with using
> vm_sev_ioctl() and have an additional variant such as
> __snp_launch_update_data() which calls into __vm_sev_ioctl() to decouple
> the ioctl from the assert for negative asserts?

Yes, this one.

> Or, do you suggest that I alter vm_sev_ioctl() to handle both positive
> and negative asserts?
> 
> Thanks!
> -Pratik
>