Re: [PATCH v7 11/14] KVM: Register/unregister the guest private memory regions

Gupta, Pankaj
2022-07-20T17:42:08Z

> Use kvm_arch_has_private_mem(), both because "has" makes it obvious this is checking
> a flag of sorts, and to align with other helpers of this nature (and with
> CONFIG_HAVE_KVM_PRIVATE_MEM).
>
> $ git grep kvm_arch | grep supported | wc -l
> 0
> $ git grep kvm_arch | grep has | wc -l
> 26
>
>>>>>>> +#ifdef CONFIG_HAVE_KVM_PRIVATE_MEM
>>>>>>> + case KVM_MEMORY_ENCRYPT_REG_REGION:
>>>>>>> + case KVM_MEMORY_ENCRYPT_UNREG_REGION: {
>>>>>>> + struct kvm_enc_region region;
>>>>>>> +
>>>>>>> + if (!kvm_arch_private_mem_supported(kvm))
>>>>>>> + goto arch_vm_ioctl;
>>>>>>> +
>>>>>>> + r = -EFAULT;
>>>>>>> + if (copy_from_user(&region, argp, sizeof(region)))
>>>>>>> + goto out;
>>>>>>> +
>>>>>>> + r = kvm_vm_ioctl_set_encrypted_region(kvm, ioctl, &region);
>>>>>>
>>>>>> this is to store private region metadata not only the encrypted region?
>>>>>
>>>>> Correct.
>>>>
>>>> Sorry for not being clear, was suggesting name change of this function from:
>>>> "kvm_vm_ioctl_set_encrypted_region" to "kvm_vm_ioctl_set_private_region"
>>>
>>> Though I don't have strong reason to change it, I'm fine with this and
>>
>> Yes, no strong reason, just thought "kvm_vm_ioctl_set_private_region" would
>> depict the actual functionality :)
>>
>>> this name matches the above kvm_arch_private_mem_supported perfectly.
>> BTW could not understand this, how "kvm_vm_ioctl_set_encrypted_region"
>> matches "kvm_arch_private_mem_supported"?
>
> Chao is saying that kvm_vm_ioctl_set_private_region() pairs nicely with
> kvm_arch_private_mem_supported(), not that the "encrypted" variant pairs nicely.
>
> I also like using "private" instead of "encrypted", though we should probably
> find a different verb than "set", because calling "set_private" when making the
> region shared is confusing. I'm struggling to come up with a good alternative
> though.
>
> kvm_vm_ioctl_set_memory_region() is already taken by KVM_SET_USER_MEMORY_REGION,
> and that also means that anything with "memory_region" in the name is bound to be
> confusing.
>
> Hmm, and if we move away from "encrypted", it probably makes sense to pass in
> addr+size instead of a kvm_enc_region.
>
> Maybe this?
>
> static int kvm_vm_ioctl_set_or_clear_mem_private(struct kvm *kvm, gpa_t gpa,
> gpa_t size, bool set_private)
>
> and then:
>
> #ifdef CONFIG_HAVE_KVM_PRIVATE_MEM
> case KVM_MEMORY_ENCRYPT_REG_REGION:
> case KVM_MEMORY_ENCRYPT_UNREG_REGION: {
> bool set = ioctl == KVM_MEMORY_ENCRYPT_REG_REGION;
> struct kvm_enc_region region;
>
> if (!kvm_arch_private_mem_supported(kvm))
> goto arch_vm_ioctl;
>
> r = -EFAULT;
> if (copy_from_user(&region, argp, sizeof(region)))
> goto out;
>
> r = kvm_vm_ioctl_set_or_clear_mem_private(kvm, region.addr,
> region.size, set);
> break;
> }
> #endif
>
> I don't love it, so if someone has a better idea...

Both the suggestions look good to me. Bring more clarity.

Thanks,
Pankaj