Re: [RFC V1 11/11] perf: Capture branch privilege information

[James Clark <james.clark@arm.com>]

On 24/01/2022 04:30, Anshuman Khandual wrote:
> Platforms like arm64 could capture privilege level information for all the
> branch records. Hence this adds a new element in the struct branch_entry to
> record the privilege level information, which could be requested through a
> new event.attr.branch_sample_type flag PERF_SAMPLE_BRANCH_PRIV_SAVE. While
> here, update the BRBE driver as required.
> 
> Cc: Will Deacon <will@kernel.org>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
> Cc: Jiri Olsa <jolsa@redhat.com>
> Cc: Namhyung Kim <namhyung@kernel.org>
> Cc: linux-arm-kernel@lists.infradead.org
> Cc: linux-perf-users@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
> ---
>  drivers/perf/arm_pmu_brbe.c              | 28 ++++++++++++++++++++++++
>  include/linux/perf_event.h               |  5 +++++
>  include/uapi/linux/perf_event.h          | 13 ++++++++++-
>  tools/include/uapi/linux/perf_event.h    | 13 ++++++++++-
>  tools/perf/Documentation/perf-record.txt |  1 +
>  tools/perf/util/parse-branch-options.c   |  1 +
>  6 files changed, 59 insertions(+), 2 deletions(-)
> 
[...]
> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> index 361fdc6b87a0..4d77710f7a4e 100644
> --- a/include/uapi/linux/perf_event.h
> +++ b/include/uapi/linux/perf_event.h
> @@ -204,6 +204,8 @@ enum perf_branch_sample_type_shift {
>  
>  	PERF_SAMPLE_BRANCH_HW_INDEX_SHIFT	= 17, /* save low level index of raw branch records */
>  
> +	PERF_SAMPLE_BRANCH_PRIV_SAVE_SHIFT	= 18, /* save privillege mode */

privillege -> privilege

> +
>  	PERF_SAMPLE_BRANCH_MAX_SHIFT		/* non-ABI */
>  };
>  
> @@ -233,6 +235,8 @@ enum perf_branch_sample_type {
>  
>  	PERF_SAMPLE_BRANCH_HW_INDEX	= 1U << PERF_SAMPLE_BRANCH_HW_INDEX_SHIFT,
>  
> +	PERF_SAMPLE_BRANCH_PRIV_SAVE	= 1U << PERF_SAMPLE_BRANCH_PRIV_SAVE_SHIFT,
> +

Can you also add the new entry to the perf verbose printer otherwise it looks like
it's not being set on branch_sample_type
(as in when using ./perf record -j any_call,u,priv -vvv):

	static void __p_branch_sample_type(char *buf, size_t size, u64 value)
	{
	#define bit_name(n) { PERF_SAMPLE_BRANCH_##n, #n }
		struct bit_names bits[] = {
			bit_name(USER), bit_name(KERNEL), bit_name(HV), bit_name(ANY),
			bit_name(ANY_CALL), bit_name(ANY_RETURN), bit_name(IND_CALL),
			bit_name(ABORT_TX), bit_name(IN_TX), bit_name(NO_TX),
			bit_name(COND), bit_name(CALL_STACK), bit_name(IND_JUMP),
			bit_name(CALL), bit_name(NO_FLAGS), bit_name(NO_CYCLES),
			bit_name(HW_INDEX),
			{ .name = NULL, }
		};
	#undef bit_name
		__p_bits(buf, size, value, bits);
	}

PERF_SAMPLE_BRANCH_TYPE_SAVE_SHIFT is also missing so it probably makes sense to add it
at the same time as that was expanded for BRBE.

>  	PERF_SAMPLE_BRANCH_MAX		= 1U << PERF_SAMPLE_BRANCH_MAX_SHIFT,
>  };
>  
> @@ -265,6 +269,12 @@ enum {
>  	PERF_BR_MAX,
>  };
>  
> +enum {
> +	PERF_BR_USER	= 0,
> +	PERF_BR_KERNEL	= 1,
> +	PERF_BR_HV	= 2,
> +};
> +
>  #define PERF_SAMPLE_BRANCH_PLM_ALL \
>  	(PERF_SAMPLE_BRANCH_USER|\
>  	 PERF_SAMPLE_BRANCH_KERNEL|\
> @@ -1377,7 +1387,8 @@ struct perf_branch_entry {
>  		abort:1,    /* transaction abort */
>  		cycles:16,  /* cycle count to last branch */
>  		type:6,     /* branch type */
> -		reserved:38;
> +		priv:2,     /* privilege level */
> +		reserved:36;
>  };
>  
>  union perf_sample_weight {
> diff --git a/tools/include/uapi/linux/perf_event.h b/tools/include/uapi/linux/perf_event.h
> index 9a82b8aaed93..a2208400b0b9 100644
> --- a/tools/include/uapi/linux/perf_event.h
> +++ b/tools/include/uapi/linux/perf_event.h
> @@ -204,6 +204,8 @@ enum perf_branch_sample_type_shift {
>  
>  	PERF_SAMPLE_BRANCH_HW_INDEX_SHIFT	= 17, /* save low level index of raw branch records */
>  
> +	PERF_SAMPLE_BRANCH_PRIV_SAVE_SHIFT	= 18, /* save privillege mode */
> +
>  	PERF_SAMPLE_BRANCH_MAX_SHIFT		/* non-ABI */
>  };
>  
> @@ -233,6 +235,8 @@ enum perf_branch_sample_type {
>  
>  	PERF_SAMPLE_BRANCH_HW_INDEX	= 1U << PERF_SAMPLE_BRANCH_HW_INDEX_SHIFT,
>  
> +	PERF_SAMPLE_BRANCH_PRIV_SAVE	= 1U << PERF_SAMPLE_BRANCH_PRIV_SAVE_SHIFT,
> +
>  	PERF_SAMPLE_BRANCH_MAX		= 1U << PERF_SAMPLE_BRANCH_MAX_SHIFT,
>  };
>  
> @@ -265,6 +269,12 @@ enum {
>  	PERF_BR_MAX,
>  };
>  
> +enum {
> +	PERF_BR_USER    = 0,
> +	PERF_BR_KERNEL  = 1,
> +	PERF_BR_HV      = 2,
> +};
> +
>  #define PERF_SAMPLE_BRANCH_PLM_ALL \
>  	(PERF_SAMPLE_BRANCH_USER|\
>  	 PERF_SAMPLE_BRANCH_KERNEL|\
> @@ -1377,7 +1387,8 @@ struct perf_branch_entry {
>  		abort:1,    /* transaction abort */
>  		cycles:16,  /* cycle count to last branch */
>  		type:6,     /* branch type */
> -		reserved:38;
> +		priv:2,     /* privilege level */
> +		reserved:36;
>  };
>  
>  union perf_sample_weight {
> diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt
> index 9ccc75935bc5..3e33686977a1 100644
> --- a/tools/perf/Documentation/perf-record.txt
> +++ b/tools/perf/Documentation/perf-record.txt
> @@ -387,6 +387,7 @@ following filters are defined:
>  	- abort_tx: only when the target is a hardware transaction abort
>  	- cond: conditional branches
>  	- save_type: save branch type during sampling in case binary is not available later
> +	- priv: save privilege state during sampling in case binary is not available later
>  
>  +
>  The option requires at least one branch type among any, any_call, any_ret, ind_call, cond.
> diff --git a/tools/perf/util/parse-branch-options.c b/tools/perf/util/parse-branch-options.c
> index bb4aa88c50a8..00588b9db474 100644
> --- a/tools/perf/util/parse-branch-options.c
> +++ b/tools/perf/util/parse-branch-options.c
> @@ -32,6 +32,7 @@ static const struct branch_mode branch_modes[] = {
>  	BRANCH_OPT("call", PERF_SAMPLE_BRANCH_CALL),
>  	BRANCH_OPT("save_type", PERF_SAMPLE_BRANCH_TYPE_SAVE),
>  	BRANCH_OPT("stack", PERF_SAMPLE_BRANCH_CALL_STACK),
> +	BRANCH_OPT("priv", PERF_SAMPLE_BRANCH_PRIV_SAVE),
>  	BRANCH_END
>  };
>  
>