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

[liwei (GF)]

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