[PATCH] lib: sbi: Bypass CY and IR bit setting in mcountinhibit

[Jessica Clarke]

On 16 Nov 2022, at 10:18, Eric Lin <eric.lin at sifive.com> wrote:
> 
> CYCLE and INSTRET counters are part of uABI and they were
> re-enable for userspace in Linux riscv pmu driver.
> 
> To make these counters increase normally in userspace, we bypass
> CY and IR bit checking when setting mcountinhibit register.
> 
> LINK:https://lore.kernel.org/all/20220928131807.30386-1-palmer@rivosinc.com/
> Signed-off-by: Eric Lin <eric.lin at sifive.com>

If Linux is making SBI calls it doesn’t want then it should stop making
those calls. S-mode requesting CY and IR inhibit bits be set is totally
legitimate in some circumstances, it’s not up to firmware to enforce a
specific S-mode OS policy.

Jess

> ---
> lib/sbi/sbi_pmu.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/sbi/sbi_pmu.c b/lib/sbi/sbi_pmu.c
> index 91d9ccc..28107e5 100644
> --- a/lib/sbi/sbi_pmu.c
> +++ b/lib/sbi/sbi_pmu.c
> @@ -318,7 +318,7 @@ static int pmu_ctr_start_hw(uint32_t cidx, uint64_t ival, bool ival_update)
> 	if (cidx >= num_hw_ctrs || cidx == 1)
> 		return SBI_EINVAL;
> 
> -	if (sbi_hart_priv_version(scratch) < SBI_HART_PRIV_VER_1_11)
> +	if (sbi_hart_priv_version(scratch) < SBI_HART_PRIV_VER_1_11 || cidx == 0 || cidx == 2)
> 		goto skip_inhibit_update;
> 
> 	/*
> @@ -413,7 +413,7 @@ static int pmu_ctr_stop_hw(uint32_t cidx)
> 	struct sbi_scratch *scratch = sbi_scratch_thishart_ptr();
> 	unsigned long mctr_inhbt;
> 
> -	if (sbi_hart_priv_version(scratch) < SBI_HART_PRIV_VER_1_11)
> +	if (sbi_hart_priv_version(scratch) < SBI_HART_PRIV_VER_1_11 || cidx == 0 || cidx == 2)
> 		return 0;
> 
> 	mctr_inhbt = csr_read(CSR_MCOUNTINHIBIT);
> -- 
> 2.36.1
> 
> 
> -- 
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