Re: [PATCH v2] Coresight: etm4x: add support for Self-hosted trace

[Suzuki K Poulose <suzuki.poulose@arm.com>]

On 09/09/2020 08:56 AM, Jonathan Zhou wrote:
> Hi Suzuki
> 
> Thanks for your review.
> 
> On 08/09/2020 17:56, Suzuki K Poulose wrote:
>> On 08/31/2020 09:02 AM, Jonathan Zhou wrote:
>>> ARMv8.4 architecture extension introduces ARMv8.4-Trace, Armv8.4
>>> Self-hosted Trace Extensions. It provides control of exception
>>> levels and security states. Let's add this feature detection and
>>> enable E1TRE and E0TRE in TRFCR_EL1 if Self-hosted Trace is
>>> supported.
>>>
>>> Cc: Catalin Marinas <catalin.marinas@arm.com>
>>> Cc: Will Deacon <will@kernel.org>
>>> Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
>>> Cc: Shaokun Zhang <zhangshaokun@hisilicon.com>
>>> Signed-off-by: Jonathan Zhou <jonathan.zhouwen@huawei.com>
>>> ---
>>>    arch/arm64/include/asm/sysreg.h               |  8 ++++++++
>>>    drivers/hwtracing/coresight/coresight-etm4x.c | 23
>>> +++++++++++++++++++++++
>>>    2 files changed, 31 insertions(+)
>>>
>>> diff --git a/arch/arm64/include/asm/sysreg.h
>>> b/arch/arm64/include/asm/sysreg.h
>>> index 554a7e8ecb07..53da5f326667 100644
>>> --- a/arch/arm64/include/asm/sysreg.h
>>> +++ b/arch/arm64/include/asm/sysreg.h
>>> @@ -184,6 +184,13 @@
>>>      #define SYS_ZCR_EL1            sys_reg(3, 0, 1, 2, 0)
>>>    +/* Trace Filter control */
>>> +#define SYS_TRFCR_EL1            sys_reg(3, 0, 1, 2, 1)
>>
>>> +/* Trace is allowed at EL0 */
>>> +#define SYS_TRFCR_EL1_E0TRE        BIT(0)
>>> +/* Trace is allowed at EL1 */
>>> +#define SYS_TRFCR_EL1_E1TRE        BIT(1)
>>> +
>>
>> Please drop SYS suffix for the fields.
>>
> Thanks, I will fix this.
> 
>>>    #define SYS_TTBR0_EL1            sys_reg(3, 0, 2, 0, 0)
>>>    #define SYS_TTBR1_EL1            sys_reg(3, 0, 2, 0, 1)
>>>    #define SYS_TCR_EL1            sys_reg(3, 0, 2, 0, 2)
>>> @@ -772,6 +779,7 @@
>>>    #define ID_AA64MMFR2_CNP_SHIFT        0
>>>      /* id_aa64dfr0 */
>>> +#define ID_AA64DFR0_SELF_HOSTED_SHIFT    40
>>>    #define ID_AA64DFR0_DOUBLELOCK_SHIFT    36
>>>    #define ID_AA64DFR0_PMSVER_SHIFT    32
>>>    #define ID_AA64DFR0_CTX_CMPS_SHIFT    28
>>> diff --git a/drivers/hwtracing/coresight/coresight-etm4x.c
>>> b/drivers/hwtracing/coresight/coresight-etm4x.c
>>> index 96425e818fc2..f72b457c2bad 100644
>>> --- a/drivers/hwtracing/coresight/coresight-etm4x.c
>>> +++ b/drivers/hwtracing/coresight/coresight-etm4x.c
>>> @@ -28,6 +28,7 @@
>>>    #include <linux/perf_event.h>
>>>    #include <linux/pm_runtime.h>
>>>    #include <linux/property.h>
>>> +#include <asm/sysreg.h>
>>>    #include <asm/sections.h>
>>>    #include <asm/local.h>
>>>    #include <asm/virt.h>
>>> @@ -785,6 +786,24 @@ static void etm4_init_arch_data(void *info)
>>>        CS_LOCK(drvdata->base);
>>>    }
>>>    +static void etm4_init_sysctrl(void *info)
>>> +{
>>> +    u64 sys_trfcr_el1, dfr0;
>>> +    int trace_filt;
>>> +
>>> +    dfr0 = read_sysreg(id_aa64dfr0_el1);
>>> +
>>> +    trace_filt = cpuid_feature_extract_unsigned_field(dfr0,
>>> +                    ID_AA64DFR0_SELF_HOSTED_SHIFT);
>>> +    /* if selfhosted trace implemented, enable trace EL0 as default. */
>>
>> What about EL1 ? We do support kernel tracing. I believe we need to do
>> this every time when we enable etm4, based on the selected config.
>>
> I don't know if it's possible to run trace sessions in a guest OS, so I
> left the EL1 and EL2 trace disabled. And it's right. We need to provide
> an interface to select these configs include the CX and TS feilds of
> TRFCR_EL2. How about a sysfs interface?

No, you don't need any additional interfaces. The etm4_config should
tell us, if the ETM4 is supposed to filter events for kernel/userspace.
We don't have virtualization support yet, so we could ignore the
TRFCR_EL2, for now.

Either we :

1) Unconditionally enable EL1 & EL0 tracing on each ETMv4 instance
at probe time and leave the trace exclusion by EL to deal with the 
kernel/userspace filtering.

OR

2) For each session of ETMv4 tracing, program the EL1 and EL0 trace
in TRFCR_EL1 based on the exclusion requested by ELs in the configs.

I prefer (1). Also, we must enable CX for TRFCR_EL2, if we are in VHE
to allow contextid tracing.

TS could be set to 0b01 in either case, to use the virtual timestamp.

Suzuki





> 
> Regards.
> Jonathan.
>>
>> Suzuki
>> .
> 


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