[RFC 3/5] KVM: Add KVM_VCPU_GET_REG_LIST.

[Rusty Russell <rusty.russell@xxxxxxxxxx>]

This is a generic interface to find out what you can use
KVM_GET_ONE_REG/KVM_SET_ONE_REG on.  Arhs need to define
KVM_HAVE_REG_LIST and then kvm_arch_num_regs() and
kvm_arch_copy_reg_indices() functions.

It's inspired by KVM_GET_MSR_INDEX_LIST, except it's a per-vcpu ioctl,
and uses 64-bit indices.

Signed-off-by: Rusty Russell <rusty.russell@xxxxxxxxxx>

diff --git a/include/linux/kvm.h b/include/linux/kvm.h
index 209b432..b607f60 100644
--- a/include/linux/kvm.h
+++ b/include/linux/kvm.h
@@ -906,7 +906,7 @@ struct kvm_s390_ucas_mapping {
 #define KVM_KVMCLOCK_CTRL	  _IO(KVMIO,   0xad)
 #define KVM_ARM_VCPU_INIT	  _IOW(KVMIO,  0xae, struct kvm_vcpu_init)
 #define KVM_VCPU_GET_MSR_INDEX_LIST    _IOWR(KVMIO, 0xaf, struct kvm_msr_list)
+#define KVM_VCPU_GET_REG_LIST	  _IOWR(KVMIO, 0xb0, struct kvm_reg_list)
 
 #define KVM_DEV_ASSIGN_ENABLE_IOMMU	(1 << 0)
 #define KVM_DEV_ASSIGN_PCI_2_3		(1 << 1)
@@ -958,4 +958,9 @@ struct kvm_assigned_msix_entry {
 	__u16 padding[3];
 };
 
+/* For KVM_VCPU_GET_REG_LIST. */
+struct kvm_reg_list {
+	__u64 n; /* number of regs */
+	__u64 reg[0];
+};
 #endif /* __LINUX_KVM_H */
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index f3d43c3..daa3838 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -572,7 +572,10 @@ int kvm_arch_set_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg);
 #define KVM_REG_LEN(index)						\
 	(1U << (((index) & KVM_REG_SIZE_MASK) >> KVM_REG_SIZE_SHIFT))
 #endif
-
+#ifdef KVM_HAVE_REG_LIST
+unsigned long kvm_arch_num_regs(struct kvm_vcpu *vcpu);
+int kvm_arch_copy_reg_indices(struct kvm_vcpu *vcpu, u64 __user *indices);
+#endif
 void kvm_free_physmem(struct kvm *kvm);
 
 void *kvm_kvzalloc(unsigned long size);
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index ad67cf4..b220c74 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1949,6 +1949,23 @@ out_free2:
 		break;
 	}
 #endif
+#ifdef KVM_HAVE_REG_LIST
+	case KVM_VCPU_GET_REG_LIST: {
+		struct kvm_reg_list __user *user_list = argp;
+		struct kvm_reg_list reg_list;
+		unsigned n;
+
+		if (copy_from_user(&reg_list, user_list, sizeof reg_list))
+			return -EFAULT;
+		n = reg_list.n;
+		reg_list.n = kvm_arch_num_regs(vcpu);
+		if (copy_to_user(user_list, &reg_list, sizeof reg_list))
+			return -EFAULT;
+		if (n < reg_list.n)
+			return -E2BIG;
+		return kvm_arch_copy_reg_indices(vcpu, user_list->reg);
+	}
+#endif
 
 	default:
 		r = kvm_arch_vcpu_ioctl(filp, ioctl, arg);
--
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