KVM: riscv: selftests: Do not start the counter in the overflow handler

There is no need to start the counter in the overflow handler as we
intend to trigger precise number of LCOFI interrupts through these
tests. The overflow irq handler has already stopped the counter. As
a result, the stop call from the test function may return already
stopped error which is fine as well.

Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Signed-off-by: Atish Patra <atishp@rivosinc.com>
Link: https://lore.kernel.org/r/20250303-kvm_pmu_improve-v2-2-41d177e45929@rivosinc.com
Signed-off-by: Anup Patel <anup@brainfault.org>

tools/testing/selftests/kvm/riscv/sbi_pmu_test.c

@@ -118,8 +118,8 @@ static void stop_counter(unsigned long counter, unsigned long stop_flags)
 
 	ret = sbi_ecall(SBI_EXT_PMU, SBI_EXT_PMU_COUNTER_STOP, counter, 1, stop_flags,
 			0, 0, 0);
-	__GUEST_ASSERT(ret.error == 0, "Unable to stop counter %ld error %ld\n",
-			       counter, ret.error);
+	__GUEST_ASSERT(ret.error == 0 || ret.error == SBI_ERR_ALREADY_STOPPED,
+		       "Unable to stop counter %ld error %ld\n", counter, ret.error);
 }
 
 static void guest_illegal_exception_handler(struct ex_regs *regs)
@@ -137,7 +137,6 @@ static void guest_irq_handler(struct ex_regs *regs)
 	unsigned int irq_num = regs->cause & ~CAUSE_IRQ_FLAG;
 	struct riscv_pmu_snapshot_data *snapshot_data = snapshot_gva;
 	unsigned long overflown_mask;
-	unsigned long counter_val = 0;
 
 	/* Validate that we are in the correct irq handler */
 	GUEST_ASSERT_EQ(irq_num, IRQ_PMU_OVF);
@@ -151,10 +150,6 @@ static void guest_irq_handler(struct ex_regs *regs)
 	GUEST_ASSERT(overflown_mask & 0x01);
 
 	WRITE_ONCE(vcpu_shared_irq_count, vcpu_shared_irq_count+1);
-
-	counter_val = READ_ONCE(snapshot_data->ctr_values[0]);
-	/* Now start the counter to mimick the real driver behavior */
-	start_counter(counter_in_use, SBI_PMU_START_FLAG_SET_INIT_VALUE, counter_val);
 }
 
 static unsigned long get_counter_index(unsigned long cbase, unsigned long cmask,