[RFC,v2,3/6] kvm: arm64: Add support for util_hint service

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index b0ff0ad700bf..38ce33564efc 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -8388,6 +8388,18 @@  must point to a byte where the value will be stored or retrieved from.
 This capability indicates that KVM supports getting the
 frequency of the current CPU that the vCPU thread is running on.
 
+8.41 KVM_CAP_UTIL_HINT
+----------------------
+
+:Architectures: arm64
+
+This capability indicates that the KVM supports taking utilization
+hints from the guest. Utilization is represented as a value from 0-1024
+where 1024 represents the highest performance point across all physical CPUs
+after normalizing for architecture. This is useful when guests are tracking
+workload on its vCPUs. Util hints allow the host to make more accurate
+frequency selections and task placement for vCPU threads.
+
 9. Known KVM API problems
 =========================
 
diff --git a/Documentation/virt/kvm/arm/index.rst b/Documentation/virt/kvm/arm/index.rst
index 47afc5c1f24a..f83877663813 100644
--- a/Documentation/virt/kvm/arm/index.rst
+++ b/Documentation/virt/kvm/arm/index.rst
@@ -12,3 +12,4 @@  ARM
    pvtime
    ptp_kvm
    get_cur_cpufreq
+   util_hint
diff --git a/Documentation/virt/kvm/arm/util_hint.rst b/Documentation/virt/kvm/arm/util_hint.rst
new file mode 100644
index 000000000000..262d142d62d9
--- /dev/null
+++ b/Documentation/virt/kvm/arm/util_hint.rst
@@ -0,0 +1,22 @@ 
+.. SPDX-License-Identifier: GPL-2.0
+
+Util_hint support for arm64
+============================
+
+Util_hint is used for sharing the utilization value from the guest
+to the host.
+
+* ARM_SMCCC_HYP_KVM_UTIL_HINT_FUNC_ID: 0x86000041
+
+This hypercall using the SMC32/HVC32 calling convention:
+
+ARM_SMCCC_HYP_KVM_UTIL_HINT_FUNC_ID
+    ==============    =========   ============================
+    Function ID:      (uint32)    0x86000041
+    Arguments:        (uint32)    util value(0-1024) where 1024 represents
+                                  the highest performance point normalized
+                                  across all CPUs
+    Return values:    (int32)     NOT_SUPPORTED(-1) on error.
+    Endianness:                   Must be the same endianness
+                                  as the host.
+    ==============    ========    ============================
diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
index ed8b63e91bdc..61309ecb7241 100644
--- a/arch/arm64/include/uapi/asm/kvm.h
+++ b/arch/arm64/include/uapi/asm/kvm.h
@@ -368,6 +368,7 @@  enum {
 	KVM_REG_ARM_VENDOR_HYP_BIT_FUNC_FEAT	= 0,
 	KVM_REG_ARM_VENDOR_HYP_BIT_PTP		= 1,
 	KVM_REG_ARM_VENDOR_HYP_BIT_GET_CUR_CPUFREQ	= 2,
+	KVM_REG_ARM_VENDOR_HYP_BIT_UTIL_HINT		= 3,
 #ifdef __KERNEL__
 	KVM_REG_ARM_VENDOR_HYP_BMAP_BIT_COUNT,
 #endif
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index f960b136c611..bf3c4d4b9b67 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -221,6 +221,7 @@  int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_PTP_KVM:
 	case KVM_CAP_ARM_SYSTEM_SUSPEND:
 	case KVM_CAP_GET_CUR_CPUFREQ:
+	case KVM_CAP_UTIL_HINT:
 		r = 1;
 		break;
 	case KVM_CAP_SET_GUEST_DEBUG2:
diff --git a/arch/arm64/kvm/hypercalls.c b/arch/arm64/kvm/hypercalls.c
index b3f4b90c024b..01dba07b5183 100644
--- a/arch/arm64/kvm/hypercalls.c
+++ b/arch/arm64/kvm/hypercalls.c
@@ -28,6 +28,20 @@  static void kvm_sched_get_cur_cpufreq(struct kvm_vcpu *vcpu, u64 *val)
 	val[0] = ret_freq;
 }
 
+static void kvm_sched_set_util(struct kvm_vcpu *vcpu, u64 *val)
+{
+	struct sched_attr attr = {
+		.sched_flags = SCHED_FLAG_UTIL_GUEST,
+	};
+	int ret;
+
+	attr.sched_util_min = smccc_get_arg1(vcpu);
+
+	ret = sched_setattr_nocheck(current, &attr);
+
+	val[0] = (u64)ret;
+}
+
 static void kvm_ptp_get_time(struct kvm_vcpu *vcpu, u64 *val)
 {
 	struct system_time_snapshot systime_snapshot;
@@ -131,6 +145,9 @@  static bool kvm_hvc_call_allowed(struct kvm_vcpu *vcpu, u32 func_id)
 	case ARM_SMCCC_VENDOR_HYP_KVM_GET_CUR_CPUFREQ_FUNC_ID:
 		return test_bit(KVM_REG_ARM_VENDOR_HYP_BIT_GET_CUR_CPUFREQ,
 				&smccc_feat->vendor_hyp_bmap);
+	case ARM_SMCCC_VENDOR_HYP_KVM_UTIL_HINT_FUNC_ID:
+		return test_bit(KVM_REG_ARM_VENDOR_HYP_BIT_UTIL_HINT,
+				&smccc_feat->vendor_hyp_bmap);
 	default:
 		return kvm_hvc_call_default_allowed(func_id);
 	}
@@ -231,6 +248,9 @@  int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)
 	case ARM_SMCCC_VENDOR_HYP_KVM_GET_CUR_CPUFREQ_FUNC_ID:
 		kvm_sched_get_cur_cpufreq(vcpu, val);
 		break;
+	case ARM_SMCCC_VENDOR_HYP_KVM_UTIL_HINT_FUNC_ID:
+		kvm_sched_set_util(vcpu, val);
+		break;
 	case ARM_SMCCC_TRNG_VERSION:
 	case ARM_SMCCC_TRNG_FEATURES:
 	case ARM_SMCCC_TRNG_GET_UUID:
diff --git a/include/linux/arm-smccc.h b/include/linux/arm-smccc.h
index e15f1bdcf3f1..9f747e5025b6 100644
--- a/include/linux/arm-smccc.h
+++ b/include/linux/arm-smccc.h
@@ -113,6 +113,7 @@ 
 #define ARM_SMCCC_KVM_FUNC_FEATURES		0
 #define ARM_SMCCC_KVM_FUNC_PTP			1
 #define ARM_SMCCC_KVM_FUNC_GET_CUR_CPUFREQ	64
+#define ARM_SMCCC_KVM_FUNC_UTIL_HINT			65
 #define ARM_SMCCC_KVM_FUNC_FEATURES_2		127
 #define ARM_SMCCC_KVM_NUM_FUNCS			128
 
@@ -145,6 +146,12 @@ 
 			   ARM_SMCCC_OWNER_VENDOR_HYP,			\
 			   ARM_SMCCC_KVM_FUNC_GET_CUR_CPUFREQ)
 
+#define ARM_SMCCC_VENDOR_HYP_KVM_UTIL_HINT_FUNC_ID			\
+	ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL,				\
+			   ARM_SMCCC_SMC_32,				\
+			   ARM_SMCCC_OWNER_VENDOR_HYP,			\
+			   ARM_SMCCC_KVM_FUNC_UTIL_HINT)
+
 /* Paravirtualised time calls (defined by ARM DEN0057A) */
 #define ARM_SMCCC_HV_PV_TIME_FEATURES				\
 	ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL,			\
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 0a1a260243bf..7f667ab344ae 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1185,6 +1185,7 @@  struct kvm_ppc_resize_hpt {
 #define KVM_CAP_DIRTY_LOG_RING_WITH_BITMAP 225
 #define KVM_CAP_PMU_EVENT_MASKED_EVENTS 226
 #define KVM_CAP_GET_CUR_CPUFREQ 512
+#define KVM_CAP_UTIL_HINT 513
 
 #ifdef KVM_CAP_IRQ_ROUTING
 
diff --git a/tools/arch/arm64/include/uapi/asm/kvm.h b/tools/arch/arm64/include/uapi/asm/kvm.h
index ed8b63e91bdc..61309ecb7241 100644
--- a/tools/arch/arm64/include/uapi/asm/kvm.h
+++ b/tools/arch/arm64/include/uapi/asm/kvm.h
@@ -368,6 +368,7 @@  enum {
 	KVM_REG_ARM_VENDOR_HYP_BIT_FUNC_FEAT	= 0,
 	KVM_REG_ARM_VENDOR_HYP_BIT_PTP		= 1,
 	KVM_REG_ARM_VENDOR_HYP_BIT_GET_CUR_CPUFREQ	= 2,
+	KVM_REG_ARM_VENDOR_HYP_BIT_UTIL_HINT		= 3,
 #ifdef __KERNEL__
 	KVM_REG_ARM_VENDOR_HYP_BMAP_BIT_COUNT,
 #endif