[RFC PATCH v2 2/4] KVM: x86: Add optional KVM_CAP_LIVE_MIGRATION and KVM_MIGRATE_CMD

[Tony Lindgren <tony.lindgren@linux.intel.com>]

Live migration of confidential guests needs the help of KVM at least for
TDX.

Add KVM_CAP_LIVE_MIGRATION for when hardware specific live migration
functions must be used.

Add KVM_MIGRATE_CMD to configure the hardware for live migration.

Assisted-by: Claude-Code:claude-opus-5 checkpatch
[ used AI to review and simplify the code ]
Signed-off-by: Tony Lindgren <tony.lindgren@linux.intel.com>
---
 arch/x86/include/asm/kvm-x86-ops.h |  2 ++
 arch/x86/include/asm/kvm_host.h    |  2 ++
 arch/x86/kvm/x86.c                 | 25 +++++++++++++++++++++++++
 include/uapi/linux/kvm.h           | 22 ++++++++++++++++++++++
 4 files changed, 51 insertions(+)

diff --git a/arch/x86/include/asm/kvm-x86-ops.h b/arch/x86/include/asm/kvm-x86-ops.h
index 83dc5086138b3..ac080b556b0c8 100644
--- a/arch/x86/include/asm/kvm-x86-ops.h
+++ b/arch/x86/include/asm/kvm-x86-ops.h
@@ -148,6 +148,8 @@ KVM_X86_OP_OPTIONAL(alloc_apic_backing_page)
 KVM_X86_OP_OPTIONAL_RET0(gmem_prepare)
 KVM_X86_OP_OPTIONAL_RET0(gmem_max_mapping_level)
 KVM_X86_OP_OPTIONAL(gmem_invalidate)
+KVM_X86_OP_OPTIONAL_RET0(cap_live_migration)
+KVM_X86_OP_OPTIONAL(migrate_cmd)
 #endif
 
 #undef KVM_X86_OP
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 5f6c1ce9673b7..d9291a8a97bb1 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -2010,6 +2010,8 @@ struct kvm_x86_ops {
 	int (*gmem_prepare)(struct kvm *kvm, kvm_pfn_t pfn, gfn_t gfn, int max_order);
 	void (*gmem_invalidate)(kvm_pfn_t start, kvm_pfn_t end);
 	int (*gmem_max_mapping_level)(struct kvm *kvm, kvm_pfn_t pfn, bool is_private);
+	bool (*cap_live_migration)(struct kvm *kvm);
+	int (*migrate_cmd)(struct kvm *kvm, struct kvm_migrate_cmd *cmd);
 };
 
 struct kvm_x86_nested_ops {
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index afcac1042947a..7064fd709e56d 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4973,6 +4973,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_READONLY_MEM:
 		r = kvm ? kvm_arch_has_readonly_mem(kvm) : 1;
 		break;
+	case KVM_CAP_LIVE_MIGRATION:
+		r = kvm ? kvm_x86_call(cap_live_migration)(kvm) : 0;
+		break;
 	default:
 		break;
 	}
@@ -7614,6 +7617,28 @@ 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_MIGRATE_CMD: {
+		struct kvm_migrate_cmd cmd;
+
+		if (!kvm_x86_ops.migrate_cmd ||
+		    !kvm_x86_call(cap_live_migration)(kvm))
+			return -ENOTTY;
+
+		if (copy_from_user(&cmd, argp, sizeof(cmd)))
+			return -EFAULT;
+
+		if (cmd.reserved || cmd.buf.reserved)
+			return -EINVAL;
+
+		r = kvm_x86_call(migrate_cmd)(kvm, &cmd);
+		if (r > 0)
+			r = -EIO;
+
+		/* Copy back also on an error to report a partially done command */
+		if (copy_to_user(argp, &cmd, sizeof(cmd)))
+			return -EFAULT;
+		break;
+	}
 	default:
 		r = -ENOTTY;
 	}
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 419011097fa8e..e5b227d3a8e40 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -997,6 +997,7 @@ struct kvm_enable_cap {
 #define KVM_CAP_S390_KEYOP 247
 #define KVM_CAP_S390_VSIE_ESAMODE 248
 #define KVM_CAP_S390_HPAGE_2G 249
+#define KVM_CAP_LIVE_MIGRATION 250
 
 struct kvm_irq_routing_irqchip {
 	__u32 irqchip;
@@ -1350,6 +1351,8 @@ struct kvm_s390_keyop {
 #define KVM_GET_DEVICE_ATTR	  _IOW(KVMIO,  0xe2, struct kvm_device_attr)
 #define KVM_HAS_DEVICE_ATTR	  _IOW(KVMIO,  0xe3, struct kvm_device_attr)
 
+#define KVM_MIGRATE_CMD		  _IOWR(KVMIO, 0xe4, struct kvm_migrate_cmd)
+
 /*
  * ioctls for vcpu fds
  */
@@ -1670,4 +1673,23 @@ struct kvm_pre_fault_memory {
 	__u64 padding[5];
 };
 
+#define KVM_MIGRATE_SETUP		0
+#define KVM_MIGRATE_ITERATION		1
+#define KVM_MIGRATE_STOP_AND_COPY	2
+#define KVM_MIGRATE_ABORT		3
+#define KVM_MIGRATE_END			4
+
+struct kvm_transfer_buffer {
+	__u64 address;
+	__u32 size;
+	__u32 reserved;
+};
+
+struct kvm_migrate_cmd {
+	__u16 command;
+	__u16 flags;
+	__u32 reserved;
+	struct kvm_transfer_buffer buf;
+};
+
 #endif /* __LINUX_KVM_H */
-- 
2.43.0