RISC-V: KVM: Implement trap & emulate for hpmcounters

As the KVM guests only see the virtual PMU counters, all hpmcounter
access should trap and KVM emulates the read access on behalf of guests.
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/include/asm/kvm_vcpu_pmu.h

@@ -44,6 +44,19 @@ struct kvm_pmu {
 #define vcpu_to_pmu(vcpu) (&(vcpu)->arch.pmu_context)
 #define pmu_to_vcpu(pmu)  (container_of((pmu), struct kvm_vcpu, arch.pmu_context))
 
+#if defined(CONFIG_32BIT)
+#define KVM_RISCV_VCPU_HPMCOUNTER_CSR_FUNCS \
+{.base = CSR_CYCLEH,	.count = 31,	.func = kvm_riscv_vcpu_pmu_read_hpm }, \
+{.base = CSR_CYCLE,	.count = 31,	.func = kvm_riscv_vcpu_pmu_read_hpm },
+#else
+#define KVM_RISCV_VCPU_HPMCOUNTER_CSR_FUNCS \
+{.base = CSR_CYCLE,	.count = 31,	.func = kvm_riscv_vcpu_pmu_read_hpm },
+#endif
+
+int kvm_riscv_vcpu_pmu_read_hpm(struct kvm_vcpu *vcpu, unsigned int csr_num,
+				unsigned long *val, unsigned long new_val,
+				unsigned long wr_mask);
+
 int kvm_riscv_vcpu_pmu_num_ctrs(struct kvm_vcpu *vcpu, struct kvm_vcpu_sbi_return *retdata);
 int kvm_riscv_vcpu_pmu_ctr_info(struct kvm_vcpu *vcpu, unsigned long cidx,
 				struct kvm_vcpu_sbi_return *retdata);
@@ -67,6 +80,9 @@ void kvm_riscv_vcpu_pmu_reset(struct kvm_vcpu *vcpu);
 struct kvm_pmu {
 };
 
+#define KVM_RISCV_VCPU_HPMCOUNTER_CSR_FUNCS \
+{.base = 0,	.count = 0,	.func = NULL },
+
 static inline void kvm_riscv_vcpu_pmu_init(struct kvm_vcpu *vcpu) {}
 static inline void kvm_riscv_vcpu_pmu_deinit(struct kvm_vcpu *vcpu) {}
 static inline void kvm_riscv_vcpu_pmu_reset(struct kvm_vcpu *vcpu) {}

arch/riscv/kvm/vcpu_insn.c

@@ -213,7 +213,9 @@ struct csr_func {
 		    unsigned long wr_mask);
 };
 
-static const struct csr_func csr_funcs[] = { };
+static const struct csr_func csr_funcs[] = {
+	KVM_RISCV_VCPU_HPMCOUNTER_CSR_FUNCS
+};
 
 /**
  * kvm_riscv_vcpu_csr_return -- Handle CSR read/write after user space

arch/riscv/kvm/vcpu_pmu.c

@@ -17,6 +17,58 @@
 
 #define kvm_pmu_num_counters(pmu) ((pmu)->num_hw_ctrs + (pmu)->num_fw_ctrs)
 
+static int pmu_ctr_read(struct kvm_vcpu *vcpu, unsigned long cidx,
+			unsigned long *out_val)
+{
+	struct kvm_pmu *kvpmu = vcpu_to_pmu(vcpu);
+	struct kvm_pmc *pmc;
+	u64 enabled, running;
+
+	pmc = &kvpmu->pmc[cidx];
+	if (!pmc->perf_event)
+		return -EINVAL;
+
+	pmc->counter_val += perf_event_read_value(pmc->perf_event, &enabled, &running);
+	*out_val = pmc->counter_val;
+
+	return 0;
+}
+
+int kvm_riscv_vcpu_pmu_read_hpm(struct kvm_vcpu *vcpu, unsigned int csr_num,
+				unsigned long *val, unsigned long new_val,
+				unsigned long wr_mask)
+{
+	struct kvm_pmu *kvpmu = vcpu_to_pmu(vcpu);
+	int cidx, ret = KVM_INSN_CONTINUE_NEXT_SEPC;
+
+	if (!kvpmu || !kvpmu->init_done) {
+		/*
+		 * In absence of sscofpmf in the platform, the guest OS may use
+		 * the legacy PMU driver to read cycle/instret. In that case,
+		 * just return 0 to avoid any illegal trap. However, any other
+		 * hpmcounter access should result in illegal trap as they must
+		 * be access through SBI PMU only.
+		 */
+		if (csr_num == CSR_CYCLE || csr_num == CSR_INSTRET) {
+			*val = 0;
+			return ret;
+		} else {
+			return KVM_INSN_ILLEGAL_TRAP;
+		}
+	}
+
+	/* The counter CSR are read only. Thus, any write should result in illegal traps */
+	if (wr_mask)
+		return KVM_INSN_ILLEGAL_TRAP;
+
+	cidx = csr_num - CSR_CYCLE;
+
+	if (pmu_ctr_read(vcpu, cidx, val) < 0)
+		return KVM_INSN_ILLEGAL_TRAP;
+
+	return ret;
+}
+
 int kvm_riscv_vcpu_pmu_num_ctrs(struct kvm_vcpu *vcpu,
 				struct kvm_vcpu_sbi_return *retdata)
 {
@@ -70,7 +122,12 @@ int kvm_riscv_vcpu_pmu_ctr_cfg_match(struct kvm_vcpu *vcpu, unsigned long ctr_ba
 int kvm_riscv_vcpu_pmu_ctr_read(struct kvm_vcpu *vcpu, unsigned long cidx,
 				struct kvm_vcpu_sbi_return *retdata)
 {
-	/* TODO */
+	int ret;
+
+	ret = pmu_ctr_read(vcpu, cidx, &retdata->out_val);
+	if (ret == -EINVAL)
+		retdata->err_val = SBI_ERR_INVALID_PARAM;
+
 	return 0;
 }