From 9c9b4ad24bf5891272679a6e994c64463db8ca03 Mon Sep 17 00:00:00 2001
From: Atish Patra <atish.patra@wdc.com>
Date: Sat, 10 Jul 2021 09:18:06 -0700
Subject: lib: sbi: Disable m/scounteren & enable mcountinhibit
Currently, all bits in mcountern are enabled unconditionally at boot time.
With SBI PMU extension, all the programmable counters should enabled only
during performance monitoring for a particular event. However, this is done
only if mcountinhibit is implemented because the supervisor mode can not
start/stop any event without mcountinhibit.
Similarly, supervisor should take care enabling scounteren which allows
U-mode to access programmable pmu counters. All the non-programmable ones
(CY, TM, IR) should be enabled in M-mode because some userspace may rely on
builtins such as __builtin_readcyclecounter. Supervisor OS can still disable
them during initial configuration.
Reviewed-by: Anup Patel <anup.patel@wdc.com>
Signed-off-by: Atish Patra <atish.patra@wdc.com>
---
lib/sbi/sbi_hart.c | 25 +++++++++++++++++++++----
1 file changed, 21 insertions(+), 4 deletions(-)
diff --git a/lib/sbi/sbi_hart.c b/lib/sbi/sbi_hart.c
index e8cd042..6254452 100644
--- a/lib/sbi/sbi_hart.c
+++ b/lib/sbi/sbi_hart.c
@@ -51,12 +51,29 @@ static void mstatus_init(struct sbi_scratch *scratch)
csr_write(CSR_MSTATUS, mstatus_val);
- /* Enable user/supervisor use of perf counters */
+ /* Disable user mode usage of all perf counters except default ones (CY, TM, IR) */
if (misa_extension('S') &&
sbi_hart_has_feature(scratch, SBI_HART_HAS_SCOUNTEREN))
- csr_write(CSR_SCOUNTEREN, -1);
- if (sbi_hart_has_feature(scratch, SBI_HART_HAS_MCOUNTEREN))
- csr_write(CSR_MCOUNTEREN, -1);
+ csr_write(CSR_SCOUNTEREN, 7);
+
+ if (sbi_hart_has_feature(scratch, SBI_HART_HAS_MCOUNTEREN)) {
+ if (sbi_hart_has_feature(scratch, SBI_HART_HAS_MCOUNTINHIBIT))
+ /**
+ * Just enable the default counters (CY, TM, IR) because
+ * some OS (e.g FreeBSD) expect them to be enabled.
+ *
+ * All other counters will be enabled at runtime after
+ * S-mode request.
+ */
+ csr_write(CSR_MCOUNTEREN, 7);
+ else
+ /* Supervisor mode usage are enabled by default */
+ csr_write(CSR_MCOUNTEREN, -1);
+ }
+
+ /* All programmable counters will start running at runtime after S-mode request */
+ if (sbi_hart_has_feature(scratch, SBI_HART_HAS_MCOUNTINHIBIT))
+ csr_write(CSR_MCOUNTINHIBIT, 0xFFFFFFF8);
/* Disable all interrupts */
csr_write(CSR_MIE, 0);
--
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