RISC-V: KVM: Add SBI PMU extension support

SBI PMU extension allows KVM guests to configure/start/stop/query
about the PMU counters in virtualized enviornment as well.

In order to allow that, KVM implements the entire SBI PMU extension.

Reviewed-by: Anup Patel <anup@brainfault.org>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Signed-off-by: Atish Patra <atishp@rivosinc.com>
Signed-off-by: Anup Patel <anup@brainfault.org>

arch/riscv/kvm/Makefile

@@ -25,4 +25,4 @@ kvm-y += vcpu_sbi_base.o
 kvm-y += vcpu_sbi_replace.o
 kvm-y += vcpu_sbi_hsm.o
 kvm-y += vcpu_timer.o
-kvm-$(CONFIG_RISCV_PMU_SBI) += vcpu_pmu.o
+kvm-$(CONFIG_RISCV_PMU_SBI) += vcpu_pmu.o vcpu_sbi_pmu.o

arch/riscv/kvm/vcpu_sbi.c

@@ -20,6 +20,16 @@ static const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_v01 = {
 };
 #endif
 
+#ifdef CONFIG_RISCV_PMU_SBI
+extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_pmu;
+#else
+static const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_pmu = {
+	.extid_start = -1UL,
+	.extid_end = -1UL,
+	.handler = NULL,
+};
+#endif
+
 static const struct kvm_vcpu_sbi_extension *sbi_ext[] = {
 	&vcpu_sbi_ext_v01,
 	&vcpu_sbi_ext_base,
@@ -28,6 +38,7 @@ static const struct kvm_vcpu_sbi_extension *sbi_ext[] = {
 	&vcpu_sbi_ext_rfence,
 	&vcpu_sbi_ext_srst,
 	&vcpu_sbi_ext_hsm,
+	&vcpu_sbi_ext_pmu,
 	&vcpu_sbi_ext_experimental,
 	&vcpu_sbi_ext_vendor,
 };

arch/riscv/kvm/vcpu_sbi_pmu.c

@@ -0,0 +1,86 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2023 Rivos Inc
+ *
+ * Authors:
+ *     Atish Patra <atishp@rivosinc.com>
+ */
+
+#include <linux/errno.h>
+#include <linux/err.h>
+#include <linux/kvm_host.h>
+#include <asm/csr.h>
+#include <asm/sbi.h>
+#include <asm/kvm_vcpu_sbi.h>
+
+static int kvm_sbi_ext_pmu_handler(struct kvm_vcpu *vcpu, struct kvm_run *run,
+				   struct kvm_vcpu_sbi_return *retdata)
+{
+	int ret = 0;
+	struct kvm_cpu_context *cp = &vcpu->arch.guest_context;
+	struct kvm_pmu *kvpmu = vcpu_to_pmu(vcpu);
+	unsigned long funcid = cp->a6;
+	u64 temp;
+
+	if (!kvpmu->init_done) {
+		retdata->err_val = SBI_ERR_NOT_SUPPORTED;
+		return 0;
+	}
+
+	switch (funcid) {
+	case SBI_EXT_PMU_NUM_COUNTERS:
+		ret = kvm_riscv_vcpu_pmu_num_ctrs(vcpu, retdata);
+		break;
+	case SBI_EXT_PMU_COUNTER_GET_INFO:
+		ret = kvm_riscv_vcpu_pmu_ctr_info(vcpu, cp->a0, retdata);
+		break;
+	case SBI_EXT_PMU_COUNTER_CFG_MATCH:
+#if defined(CONFIG_32BIT)
+		temp = ((uint64_t)cp->a5 << 32) | cp->a4;
+#else
+		temp = cp->a4;
+#endif
+		/*
+		 * This can fail if perf core framework fails to create an event.
+		 * Forward the error to userspace because it's an error which
+		 * happened within the host kernel. The other option would be
+		 * to convert to an SBI error and forward to the guest.
+		 */
+		ret = kvm_riscv_vcpu_pmu_ctr_cfg_match(vcpu, cp->a0, cp->a1,
+						       cp->a2, cp->a3, temp, retdata);
+		break;
+	case SBI_EXT_PMU_COUNTER_START:
+#if defined(CONFIG_32BIT)
+		temp = ((uint64_t)cp->a4 << 32) | cp->a3;
+#else
+		temp = cp->a3;
+#endif
+		ret = kvm_riscv_vcpu_pmu_ctr_start(vcpu, cp->a0, cp->a1, cp->a2,
+						   temp, retdata);
+		break;
+	case SBI_EXT_PMU_COUNTER_STOP:
+		ret = kvm_riscv_vcpu_pmu_ctr_stop(vcpu, cp->a0, cp->a1, cp->a2, retdata);
+		break;
+	case SBI_EXT_PMU_COUNTER_FW_READ:
+		ret = kvm_riscv_vcpu_pmu_ctr_read(vcpu, cp->a0, retdata);
+		break;
+	default:
+		retdata->err_val = SBI_ERR_NOT_SUPPORTED;
+	}
+
+	return ret;
+}
+
+static unsigned long kvm_sbi_ext_pmu_probe(struct kvm_vcpu *vcpu)
+{
+	struct kvm_pmu *kvpmu = vcpu_to_pmu(vcpu);
+
+	return kvpmu->init_done;
+}
+
+const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_pmu = {
+	.extid_start = SBI_EXT_PMU,
+	.extid_end = SBI_EXT_PMU,
+	.handler = kvm_sbi_ext_pmu_handler,
+	.probe = kvm_sbi_ext_pmu_probe,
+};