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

On Thu, Jul 21, 2022 at 03:34:59PM +0800, Wei Wang wrote:

On 7/21/22 00:21, Sean Christopherson wrote:

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On Wed, Jul 20, 2022, Gupta, Pankaj wrote:

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+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

Make sense. kvm_arch_has_private_mem it actually better.

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+#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 :)

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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.

This makes sense.

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Maybe this?

static int kvm_vm_ioctl_set_or_clear_mem_private(struct kvm *kvm, gpa_t gpa,
					         gpa_t size, bool set_private)

Currently this should work.

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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...

Maybe you could tag it with cgs for all the confidential guest support
related stuff:
e.g. kvm_vm_ioctl_set_cgs_mem()

bool is_private = ioctl == KVM_MEMORY_ENCRYPT_REG_REGION;
...
kvm_vm_ioctl_set_cgs_mem(, is_private)

If we plan to widely use such abbr. through KVM (e.g. it's well known),
I'm fine.

I actually use mem_attr in patch: https://lkml.org/lkml/2022/7/20/610
But I also don't quite like it, it's so generic and sounds say nothing.

But I do want a name can cover future usages other than just 
private/shared (pKVM for example may have a third state).

Thanks,
Chao