Re: [PATCH] target/arm: read access to performance counters from EL0

[Alex Zuepke]

Hi,

wanted to ping again on this issue before it gets lost.

Am 28.04.22 um 15:27 schrieb Alex Zuepke:
> The ARMv8 manual defines that PMUSERENR_EL0.ER enables read-access
> to both PMXEVCNTR_EL0 and PMEVCNTR<n>_EL0 registers, however,
> we only use it for PMXEVCNTR_EL0. Extend to PMEVCNTR<n>_EL0 as well.

I configure PMUSERENR_EL0.ER for read access to the performance counters 
in user space, but it only works when I use the indexed access via the 
PMXEVCNTR_EL0 register, and not the direct access via the 
PMEVCNTR<n>_EL0 registers.

Real Cortex-A53:
PMXEVCNTR_EL0    read access in user space OK
PMEVCNTR<n>_EL0  read access works

QEMU:
PMXEVCNTR_EL0    read access works
PMEVCNTR<n>_EL0  exception

The patch changes the access function for 32-bit mode PMEVCNTR<n> and 
64-bit mode PMEVCNTR<n>_EL0 registers to the one from the "X" variant.


Best regards
Alex


> Signed-off-by: Alex Zuepke <alex.zuepke@tum.de>
> ---
>   target/arm/helper.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/target/arm/helper.c b/target/arm/helper.c
> index 63397bbac1..eb42b22766 100644
> --- a/target/arm/helper.c
> +++ b/target/arm/helper.c
> @@ -6679,10 +6679,10 @@ static void define_pmu_regs(ARMCPU *cpu)
>                 .crm = 8 | (3 & (i >> 3)), .opc1 = 0, .opc2 = i & 7,
>                 .access = PL0_RW, .type = ARM_CP_IO | ARM_CP_ALIAS,
>                 .readfn = pmevcntr_readfn, .writefn = pmevcntr_writefn,
> -              .accessfn = pmreg_access },
> +              .accessfn = pmreg_access_xevcntr },
>               { .name = pmevcntr_el0_name, .state = ARM_CP_STATE_AA64,
>                 .opc0 = 3, .opc1 = 3, .crn = 14, .crm = 8 | (3 & (i >> 3)),
> -              .opc2 = i & 7, .access = PL0_RW, .accessfn = pmreg_access,
> +              .opc2 = i & 7, .access = PL0_RW, .accessfn = 
> pmreg_access_xevcntr,
>                 .type = ARM_CP_IO,
>                 .readfn = pmevcntr_readfn, .writefn = pmevcntr_writefn,
>                 .raw_readfn = pmevcntr_rawread,