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

[Sean Christopherson]

On Wed, Jul 20, 2022, Gupta, Pankaj wrote:
> 
> > > > > > +bool __weak kvm_arch_private_mem_supported(struct kvm *kvm)

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...