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

Sean Christopherson
2022-07-20T16:21:47Z

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...