Re: [PATCH v2] drivers/perf: Add support for ARMv8.3-SPE

From: liwei (GF)
Date: Thu Nov 19 2020 - 09:58:05 EST


Hi Will,

On 2020/10/2 18:57, Will Deacon wrote:
> On Wed, Sep 30, 2020 at 05:31:35PM +0800, Wei Li wrote:
>> Armv8.3 extends the SPE by adding:
>> - Alignment field in the Events packet, and filtering on this event
>> using PMSEVFR_EL1.
>> - Support for the Scalable Vector Extension (SVE).
>>
>> The main additions for SVE are:
>> - Recording the vector length for SVE operations in the Operation Type
>> packet. It is not possible to filter on vector length.
>> - Incomplete predicate and empty predicate fields in the Events packet,
>> and filtering on these events using PMSEVFR_EL1.
>>
>> Update the check of pmsevfr for empty/partial predicated SVE and
>> alignment event in SPE driver. For adaption by the version of SPE,
>> expose 'pmsver' as cap attribute to userspace.
>>
>> Signed-off-by: Wei Li <liwei391@xxxxxxxxxx>
>> ---
>> v1 -> v2:
>> - Rename 'pmuver' to 'pmsver', change it's type to 'u16' from 'int'.
>> (Suggested by Will and Leo.)
>> - Expose 'pmsver' as cap attribute through sysfs, instead of printing.
>> (Suggested by Will.)
>> ---
>> arch/arm64/include/asm/sysreg.h | 4 +++-
>> drivers/perf/arm_spe_pmu.c | 18 ++++++++++++++++--
>> 2 files changed, 19 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
>> index 554a7e8ecb07..f4f9c1fc6398 100644
>> --- a/arch/arm64/include/asm/sysreg.h
>> +++ b/arch/arm64/include/asm/sysreg.h
>> @@ -281,7 +281,6 @@
>> #define SYS_PMSFCR_EL1_ST_SHIFT 18
>>
>> #define SYS_PMSEVFR_EL1 sys_reg(3, 0, 9, 9, 5)
>> -#define SYS_PMSEVFR_EL1_RES0 0x0000ffff00ff0f55UL
>>
>> #define SYS_PMSLATFR_EL1 sys_reg(3, 0, 9, 9, 6)
>> #define SYS_PMSLATFR_EL1_MINLAT_SHIFT 0
>> @@ -787,6 +786,9 @@
>> #define ID_AA64DFR0_PMUVER_8_5 0x6
>> #define ID_AA64DFR0_PMUVER_IMP_DEF 0xf
>>
>> +#define ID_AA64DFR0_PMSVER_8_2 0x1
>> +#define ID_AA64DFR0_PMSVER_8_3 0x2
>> +
>> #define ID_DFR0_PERFMON_SHIFT 24
>>
>> #define ID_DFR0_PERFMON_8_1 0x4
>> diff --git a/drivers/perf/arm_spe_pmu.c b/drivers/perf/arm_spe_pmu.c
>> index cc00915ad6d1..52e7869f5621 100644
>> --- a/drivers/perf/arm_spe_pmu.c
>> +++ b/drivers/perf/arm_spe_pmu.c
>> @@ -54,7 +54,7 @@ struct arm_spe_pmu {
>> struct hlist_node hotplug_node;
>>
>> int irq; /* PPI */
>> -
>> + u16 pmsver;
>> u16 min_period;
>> u16 counter_sz;
>>
>> @@ -80,6 +80,15 @@ struct arm_spe_pmu {
>> /* Keep track of our dynamic hotplug state */
>> static enum cpuhp_state arm_spe_pmu_online;
>>
>> +static u64 sys_pmsevfr_el1_mask[] = {
>> + [ID_AA64DFR0_PMSVER_8_2] = GENMASK_ULL(63, 48) | GENMASK_ULL(31, 24) |
>> + GENMASK_ULL(15, 12) | BIT_ULL(7) | BIT_ULL(5) | BIT_ULL(3) |
>> + BIT_ULL(1),
>> + [ID_AA64DFR0_PMSVER_8_3] = GENMASK_ULL(63, 48) | GENMASK_ULL(31, 24) |
>> + GENMASK_ULL(18, 17) | GENMASK_ULL(15, 11) | BIT_ULL(7) |
>> + BIT_ULL(5) | BIT_ULL(3) | BIT_ULL(1),
>> +};
>
> Ok, so I finally figured out what I don't like about this: it's the fact
> that the RES0 mask only ever reduces, but we have no way of ensuring that
> by construction with this approach. In other words, it's a bit brittle to
> keep all of these things defined entirely separately from one another.
>
> How about a small change so that we define things like:
>
> #define SYS_PMSEVFR_EL1_RES0_8_2 SYS_PMSEVFR_EL1_RES0 &
> ~(...)
>
> #define SYS_PMSEVFR_EL1_RES0_8_3 SYS_PMSEVFR_EL1_RES0_8_2 &
> ~(...)
>
> where the '...' parts identify the bits that are no longer RES0 for that
> version of the architecture?
>

Sorry for the long delay.

These is also an array-index-out-of-bounds issue when accessing 'sys_pmsevfr_el1_mask', if
the pmsver read in the future is bigger than what the driver supports.

So how about change to:

static u64 arm_spe_pmsevfr_mask(u16 pmsver)
{
u64 mask = 0;

if (pmsver >= ID_AA64DFR0_PMSVER_8_3)
mask |= BIT_ULL(18) | BIT_ULL(17) | BIT_ULL(11);
if (pmsver >= ID_AA64DFR0_PMSVER_8_2)
mask |= GENMASK_ULL(63, 48) | GENMASK_ULL(31, 24) |
GENMASK_ULL(15, 12) | BIT_ULL(7) | BIT_ULL(5) | BIT_ULL(3) |
BIT_ULL(1);
return mask;
}

Thus, the driver can try its best to support, and the definition is clear enough to show
the difference between versions of SPE.

Or should i still define them as what you advised and add a check of pmsver to just serve
the versions what the driver support?

Thanks,
Wei