[PATCH v13 018/113] KVM: x86, tdx: Make KVM_CAP_MAX_VCPUS backend specific

[isaku . yamahata]

From: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>

TDX has its own limitation on the maximum number of vcpus that the guest
can accommodate.  Allow x86 kvm backend to implement its own KVM_ENABLE_CAP
handler and implement TDX backend for KVM_CAP_MAX_VCPUS.  user space VMM,
e.g. qemu, can specify its value instead of KVM_MAX_VCPUS.

Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
---
 arch/x86/include/asm/kvm-x86-ops.h |  2 ++
 arch/x86/include/asm/kvm_host.h    |  2 ++
 arch/x86/kvm/vmx/main.c            | 22 ++++++++++++++++++++++
 arch/x86/kvm/vmx/tdx.c             | 30 ++++++++++++++++++++++++++++++
 arch/x86/kvm/vmx/tdx.h             |  3 +++
 arch/x86/kvm/vmx/x86_ops.h         |  2 ++
 arch/x86/kvm/x86.c                 |  4 ++++
 7 files changed, 65 insertions(+)

diff --git a/arch/x86/include/asm/kvm-x86-ops.h b/arch/x86/include/asm/kvm-x86-ops.h
index 58fbaa05fc8c..7522c193f2b4 100644
--- a/arch/x86/include/asm/kvm-x86-ops.h
+++ b/arch/x86/include/asm/kvm-x86-ops.h
@@ -21,6 +21,8 @@ KVM_X86_OP(hardware_unsetup)
 KVM_X86_OP(has_emulated_msr)
 KVM_X86_OP(vcpu_after_set_cpuid)
 KVM_X86_OP(is_vm_type_supported)
+KVM_X86_OP_OPTIONAL(max_vcpus);
+KVM_X86_OP_OPTIONAL(vm_enable_cap)
 KVM_X86_OP(vm_init)
 KVM_X86_OP_OPTIONAL(vm_destroy)
 KVM_X86_OP_OPTIONAL_RET0(vcpu_precreate)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 49e3ca89aced..d98d61e5213d 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1562,7 +1562,9 @@ struct kvm_x86_ops {
 	void (*vcpu_after_set_cpuid)(struct kvm_vcpu *vcpu);
 
 	bool (*is_vm_type_supported)(unsigned long vm_type);
+	int (*max_vcpus)(struct kvm *kvm);
 	unsigned int vm_size;
+	int (*vm_enable_cap)(struct kvm *kvm, struct kvm_enable_cap *cap);
 	int (*vm_init)(struct kvm *kvm);
 	void (*vm_destroy)(struct kvm *kvm);
 
diff --git a/arch/x86/kvm/vmx/main.c b/arch/x86/kvm/vmx/main.c
index 8ddd263eeabc..68bb320d0b6d 100644
--- a/arch/x86/kvm/vmx/main.c
+++ b/arch/x86/kvm/vmx/main.c
@@ -6,6 +6,7 @@
 #include "nested.h"
 #include "pmu.h"
 #include "tdx.h"
+#include "tdx_arch.h"
 
 static bool enable_tdx __ro_after_init;
 module_param_named(tdx, enable_tdx, bool, 0444);
@@ -29,6 +30,17 @@ static bool vt_is_vm_type_supported(unsigned long type)
 		(enable_tdx && tdx_is_vm_type_supported(type));
 }
 
+static int vt_max_vcpus(struct kvm *kvm)
+{
+	if (!kvm)
+		return KVM_MAX_VCPUS;
+
+	if (is_td(kvm))
+		return min3(kvm->max_vcpus, KVM_MAX_VCPUS, TDX_MAX_VCPUS);
+
+	return kvm->max_vcpus;
+}
+
 static __init int vt_hardware_setup(void)
 {
 	int ret;
@@ -42,6 +54,14 @@ static __init int vt_hardware_setup(void)
 	return 0;
 }
 
+static int vt_vm_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap)
+{
+	if (is_td(kvm))
+		return tdx_vm_enable_cap(kvm, cap);
+
+	return -EINVAL;
+}
+
 static int vt_vm_init(struct kvm *kvm)
 {
 	if (is_td(kvm))
@@ -81,7 +101,9 @@ struct kvm_x86_ops vt_x86_ops __initdata = {
 	.has_emulated_msr = vmx_has_emulated_msr,
 
 	.is_vm_type_supported = vt_is_vm_type_supported,
+	.max_vcpus = vt_max_vcpus,
 	.vm_size = sizeof(struct kvm_vmx),
+	.vm_enable_cap = vt_vm_enable_cap,
 	.vm_init = vt_vm_init,
 	.vm_destroy = vmx_vm_destroy,
 
diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index d759028a698e..8b02e605cfb5 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -16,6 +16,36 @@
 		offsetof(struct tdsysinfo_struct, cpuid_configs))	\
 		/ sizeof(struct tdx_cpuid_config))
 
+int tdx_vm_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap)
+{
+	int r;
+
+	switch (cap->cap) {
+	case KVM_CAP_MAX_VCPUS: {
+		if (cap->flags || cap->args[0] == 0)
+			return -EINVAL;
+		if (cap->args[0] > KVM_MAX_VCPUS)
+			return -E2BIG;
+		if (cap->args[0] > TDX_MAX_VCPUS)
+			return -E2BIG;
+
+		mutex_lock(&kvm->lock);
+		if (kvm->created_vcpus)
+			r = -EBUSY;
+		else {
+			kvm->max_vcpus = cap->args[0];
+			r = 0;
+		}
+		mutex_unlock(&kvm->lock);
+		break;
+	}
+	default:
+		r = -EINVAL;
+		break;
+	}
+	return r;
+}
+
 int tdx_hardware_enable(void)
 {
 	return tdx_cpu_enable();
diff --git a/arch/x86/kvm/vmx/tdx.h b/arch/x86/kvm/vmx/tdx.h
index 2210c8c1e893..3860aa351bd9 100644
--- a/arch/x86/kvm/vmx/tdx.h
+++ b/arch/x86/kvm/vmx/tdx.h
@@ -3,6 +3,9 @@
 #define __KVM_X86_TDX_H
 
 #ifdef CONFIG_INTEL_TDX_HOST
+
+#include "tdx_ops.h"
+
 struct kvm_tdx {
 	struct kvm kvm;
 	/* TDX specific members follow. */
diff --git a/arch/x86/kvm/vmx/x86_ops.h b/arch/x86/kvm/vmx/x86_ops.h
index c70749114e9e..8118647aa8ca 100644
--- a/arch/x86/kvm/vmx/x86_ops.h
+++ b/arch/x86/kvm/vmx/x86_ops.h
@@ -143,6 +143,7 @@ int tdx_hardware_enable(void);
 bool tdx_is_vm_type_supported(unsigned long type);
 int tdx_dev_ioctl(void __user *argp);
 
+int tdx_vm_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap);
 int tdx_vm_ioctl(struct kvm *kvm, void __user *argp);
 #else
 static inline int tdx_hardware_setup(struct kvm_x86_ops *x86_ops) { return -ENOSYS; }
@@ -150,6 +151,7 @@ static inline int tdx_hardware_enable(void) { return -EOPNOTSUPP; }
 static inline bool tdx_is_vm_type_supported(unsigned long type) { return false; }
 static inline int tdx_dev_ioctl(void __user *argp) { return -EOPNOTSUPP; };
 
+static inline int tdx_vm_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap) { return -EINVAL; };
 static inline int tdx_vm_ioctl(struct kvm *kvm, void __user *argp) { return -EOPNOTSUPP; }
 #endif
 
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 8687623929c3..7b02dd40ef21 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4500,6 +4500,8 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 		break;
 	case KVM_CAP_MAX_VCPUS:
 		r = KVM_MAX_VCPUS;
+		if (kvm_x86_ops.max_vcpus)
+			r = static_call(kvm_x86_max_vcpus)(kvm);
 		break;
 	case KVM_CAP_MAX_VCPU_ID:
 		r = KVM_MAX_VCPU_IDS;
@@ -6439,6 +6441,8 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
 		break;
 	default:
 		r = -EINVAL;
+		if (kvm_x86_ops.vm_enable_cap)
+			r = static_call(kvm_x86_vm_enable_cap)(kvm, cap);
 		break;
 	}
 	return r;
-- 
2.25.1