Handle KVM_GET_{SUPPORTED,EMULATED}_CPUID in kvm_arch_vm_ioctl()
so that userspace can query supported CPUID on a VM fd.

When issued on a VM fd, KVM can return CPUID data tailored to the VM's
type (e.g. using the TDX overlay for TDX VMs instead of the default
VMX overlay).  @kvm is not yet used to select the overlay; a follow-on
patch will wire that up.  The dev-ioctl path continues to work by
passing NULL for @kvm.

Extract the copy_from_user/copy_to_user boilerplate into a shared
helper, kvm_get_cpuid(), used by both the dev-ioctl and VM-ioctl
paths.

There will a be new capability added for CPUID paranoid mode in a later
patch, reuse that capability to tell userspace that the VM versions of
KVM_GET_{SUPPORTED,EMULATED}_CPUID are supported.

Signed-off-by: Binbin Wu <binbin.wu@linux.intel.com>
---
 arch/x86/kvm/cpuid.c |  7 ++++---
 arch/x86/kvm/cpuid.h |  6 +++---
 arch/x86/kvm/x86.c   | 42 ++++++++++++++++++++++++++----------------
 3 files changed, 33 insertions(+), 22 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 938b19767feb..9634ea01d2a3 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -2013,9 +2013,10 @@ static bool sanity_check_entries(struct kvm_cpuid_entry2 __user *entries,
 	return false;
 }
 
-int kvm_dev_ioctl_get_cpuid(struct kvm_cpuid2 *cpuid,
-			    struct kvm_cpuid_entry2 __user *entries,
-			    unsigned int type)
+/* The input kvm could be NULL, check it before using. */
+int kvm_vm_ioctl_get_cpuid(struct kvm *kvm, struct kvm_cpuid2 *cpuid,
+			   struct kvm_cpuid_entry2 __user *entries,
+			   unsigned int type)
 {
 	static const u32 funcs[] = {
 		0, 0x80000000, CENTAUR_CPUID_SIGNATURE, KVM_CPUID_SIGNATURE,
diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
index 4b1274f055e5..0afde541b036 100644
--- a/arch/x86/kvm/cpuid.h
+++ b/arch/x86/kvm/cpuid.h
@@ -74,9 +74,9 @@ static inline struct kvm_cpuid_entry2 *kvm_find_cpuid_entry(struct kvm_vcpu *vcp
 				     function, KVM_CPUID_INDEX_NOT_SIGNIFICANT);
 }
 
-int kvm_dev_ioctl_get_cpuid(struct kvm_cpuid2 *cpuid,
-			    struct kvm_cpuid_entry2 __user *entries,
-			    unsigned int type);
+int kvm_vm_ioctl_get_cpuid(struct kvm *kvm, struct kvm_cpuid2 *cpuid,
+			   struct kvm_cpuid_entry2 __user *entries,
+			   unsigned int type);
 int kvm_vcpu_ioctl_set_cpuid(struct kvm_vcpu *vcpu,
 			     struct kvm_cpuid *cpuid,
 			     struct kvm_cpuid_entry __user *entries);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index db8434f9a2ee..525fcb09a4c0 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5041,6 +5041,26 @@ static int kvm_x86_dev_has_attr(struct kvm_device_attr *attr)
 	return __kvm_x86_dev_get_attr(attr, &val);
 }
 
+static int kvm_x86_vm_get_cpuid(struct kvm *kvm, void __user *argp, unsigned int ioctl)
+{
+	struct kvm_cpuid2 __user *cpuid_arg = argp;
+	struct kvm_cpuid2 cpuid;
+	int r = -EFAULT;
+
+	if (copy_from_user(&cpuid, cpuid_arg, sizeof(cpuid)))
+		return r;
+
+	r = kvm_vm_ioctl_get_cpuid(kvm, &cpuid, cpuid_arg->entries, ioctl);
+	if (r)
+		return r;
+
+	r = -EFAULT;
+	if (copy_to_user(cpuid_arg, &cpuid, sizeof(cpuid)))
+		return r;
+
+	return 0;
+}
+
 long kvm_arch_dev_ioctl(struct file *filp,
 			unsigned int ioctl, unsigned long arg)
 {
@@ -5076,22 +5096,7 @@ long kvm_arch_dev_ioctl(struct file *filp,
 	}
 	case KVM_GET_SUPPORTED_CPUID:
 	case KVM_GET_EMULATED_CPUID: {
-		struct kvm_cpuid2 __user *cpuid_arg = argp;
-		struct kvm_cpuid2 cpuid;
-
-		r = -EFAULT;
-		if (copy_from_user(&cpuid, cpuid_arg, sizeof(cpuid)))
-			goto out;
-
-		r = kvm_dev_ioctl_get_cpuid(&cpuid, cpuid_arg->entries,
-					    ioctl);
-		if (r)
-			goto out;
-
-		r = -EFAULT;
-		if (copy_to_user(cpuid_arg, &cpuid, sizeof(cpuid)))
-			goto out;
-		r = 0;
+		r = kvm_x86_vm_get_cpuid(NULL, argp, ioctl);
 		break;
 	}
 	case KVM_X86_GET_MCE_CAP_SUPPORTED:
@@ -7628,6 +7633,11 @@ int kvm_arch_vm_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg)
 		r = kvm_vm_ioctl_set_msr_filter(kvm, &filter);
 		break;
 	}
+	case KVM_GET_SUPPORTED_CPUID:
+	case KVM_GET_EMULATED_CPUID: {
+		r = kvm_x86_vm_get_cpuid(kvm, argp, ioctl);
+		break;
+	}
 	default:
 		r = -ENOTTY;
 	}
-- 
2.46.0