Re: [RFC PATCH v11 12/29] KVM: Add KVM_CREATE_GUEST_MEMFD ioctl() for guest-specific backing memory

[Xiaoyao Li]

On 7/19/2023 7:44 AM, Sean Christopherson wrote:
> @@ -5134,6 +5167,16 @@ static long kvm_vm_ioctl(struct file *filp,
>   	case KVM_GET_STATS_FD:
>   		r = kvm_vm_ioctl_get_stats_fd(kvm);
>   		break;
> +	case KVM_CREATE_GUEST_MEMFD: {
> +		struct kvm_create_guest_memfd guest_memfd;
> +
> +		r = -EFAULT;
> +		if (copy_from_user(&guest_memfd, argp, sizeof(guest_memfd)))
> +			goto out;
> +
> +		r = kvm_gmem_create(kvm, &guest_memfd);
> +		break;
> +	}

Does it need a new CAP to indicate the support of guest_memfd?

This is patch series introduces 3 new CAPs and it seems any one of them 
can serve as the indicator of guest_memfd.

+#define KVM_CAP_USER_MEMORY2 230
+#define KVM_CAP_MEMORY_ATTRIBUTES 231
+#define KVM_CAP_VM_TYPES 232

or we just go and try the ioctl, the return value will tell the result?