RISC-V: KVM: No need to exit to the user space if perf event failed

Currently, we return a linux error code if creating a perf event failed
in kvm. That shouldn't be necessary as guest can continue to operate
without perf profiling or profiling with firmware counters.

Return appropriate SBI error code to indicate that PMU configuration
failed. An error message in kvm already describes the reason for failure.

Fixes: 0cb74b6 ("RISC-V: KVM: Implement perf support without sampling")
Reviewed-by: Anup Patel <anup@brainfault.org>
Signed-off-by: Atish Patra <atishp@rivosinc.com>
Link: https://lore.kernel.org/r/20240420151741.962500-13-atishp@rivosinc.com
Signed-off-by: Anup Patel <anup@brainfault.org>

arch/riscv/kvm/vcpu_pmu.c

@@ -229,8 +229,9 @@ static int kvm_pmu_validate_counter_mask(struct kvm_pmu *kvpmu, unsigned long ct
 	return 0;
 }
 
-static int kvm_pmu_create_perf_event(struct kvm_pmc *pmc, struct perf_event_attr *attr,
-				     unsigned long flags, unsigned long eidx, unsigned long evtdata)
+static long kvm_pmu_create_perf_event(struct kvm_pmc *pmc, struct perf_event_attr *attr,
+				      unsigned long flags, unsigned long eidx,
+				      unsigned long evtdata)
 {
 	struct perf_event *event;
 
@@ -454,7 +455,8 @@ int kvm_riscv_vcpu_pmu_ctr_cfg_match(struct kvm_vcpu *vcpu, unsigned long ctr_ba
 				     unsigned long eidx, u64 evtdata,
 				     struct kvm_vcpu_sbi_return *retdata)
 {
-	int ctr_idx, ret, sbiret = 0;
+	int ctr_idx, sbiret = 0;
+	long ret;
 	bool is_fevent;
 	unsigned long event_code;
 	u32 etype = kvm_pmu_get_perf_event_type(eidx);
@@ -513,8 +515,10 @@ int kvm_riscv_vcpu_pmu_ctr_cfg_match(struct kvm_vcpu *vcpu, unsigned long ctr_ba
 			kvpmu->fw_event[event_code].started = true;
 	} else {
 		ret = kvm_pmu_create_perf_event(pmc, &attr, flags, eidx, evtdata);
-		if (ret)
-			return ret;
+		if (ret) {
+			sbiret = SBI_ERR_NOT_SUPPORTED;
+			goto out;
+		}
 	}
 
 	set_bit(ctr_idx, kvpmu->pmc_in_use);

arch/riscv/kvm/vcpu_sbi_pmu.c

@@ -42,9 +42,9 @@ static int kvm_sbi_ext_pmu_handler(struct kvm_vcpu *vcpu, struct kvm_run *run,
 #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.
+		 * No need to forward the error to userspace and exit the guest.
+		 * The operation can continue without profiling. Forward the
+		 * appropriate SBI error to the guest.
 		 */
 		ret = kvm_riscv_vcpu_pmu_ctr_cfg_match(vcpu, cp->a0, cp->a1,
 						       cp->a2, cp->a3, temp, retdata);