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Message-ID: <e513b32f-78fb-46d2-90e1-e7868bffa368@amperemail.onmicrosoft.com>
Date: Thu, 12 Jun 2025 23:19:54 -0400
From: Adam Young <admiyo@...eremail.onmicrosoft.com>
To: "Rob Herring (Arm)" <robh@...nel.org>, Will Deacon <will@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Catalin Marinas <catalin.marinas@....com>, Jonathan Corbet <corbet@....net>,
Marc Zyngier <maz@...nel.org>, Oliver Upton <oliver.upton@...ux.dev>,
Joey Gouly <joey.gouly@....com>, Suzuki K Poulose <suzuki.poulose@....com>,
Zenghui Yu <yuzenghui@...wei.com>, James Clark <james.clark@...aro.org>,
Anshuman Khandual <anshuman.khandual@....com>, Leo Yan <leo.yan@....com>
Cc: linux-arm-kernel@...ts.infradead.org, linux-perf-users@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
kvmarm@...ts.linux.dev
Subject: Re: [PATCH v23 4/4] perf: arm_pmuv3: Add support for the Branch
Record Buffer Extension (BRBE)
On 6/11/25 14:01, Rob Herring (Arm) wrote:
> The ARMv9.2 architecture introduces the optional Branch Record Buffer
> Extension (BRBE), which records information about branches as they are
> executed into set of branch record registers. BRBE is similar to x86's
> Last Branch Record (LBR) and PowerPC's Branch History Rolling Buffer
> (BHRB).
>
> BRBE supports filtering by exception level and can filter just the
> source or target address if excluded to avoid leaking privileged
> addresses. The h/w filter would be sufficient except when there are
> multiple events with disjoint filtering requirements. In this case, BRBE
> is configured with a union of all the events' desired branches, and then
> the recorded branches are filtered based on each event's filter. For
> example, with one event capturing kernel events and another event
> capturing user events, BRBE will be configured to capture both kernel
> and user branches. When handling event overflow, the branch records have
> to be filtered by software to only include kernel or user branch
> addresses for that event. In contrast, x86 simply configures LBR using
> the last installed event which seems broken.
>
> It is possible on x86 to configure branch filter such that no branches
> are ever recorded (e.g. -j save_type). For BRBE, events with a
> configuration that will result in no samples are rejected.
>
> Recording branches in KVM guests is not supported like x86. However,
> perf on x86 allows requesting branch recording in guests. The guest
> events are recorded, but the resulting branches are all from the host.
> For BRBE, events with branch recording and "exclude_host" set are
> rejected. Requiring "exclude_guest" to be set did not work. The default
> for the perf tool does set "exclude_guest" if no exception level
> options are specified. However, specifying kernel or user events
> defaults to including both host and guest. In this case, only host
> branches are recorded.
>
> BRBE can support some additional exception branch types compared to
> x86. On x86, all exceptions other than syscalls are recorded as IRQ.
> With BRBE, it is possible to better categorize these exceptions. One
> limitation relative to x86 is we cannot distinguish a syscall return
> from other exception returns. So all exception returns are recorded as
> ERET type. The FIQ branch type is omitted as the only FIQ user is Apple
> platforms which don't support BRBE. The debug branch types are omitted
> as there is no clear need for them.
>
> BRBE records are invalidated whenever events are reconfigured, a new
> task is scheduled in, or after recording is paused (and the records
> have been recorded for the event). The architecture allows branch
> records to be invalidated by the PE under implementation defined
> conditions. It is expected that these conditions are rare.
>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Co-developed-by: Anshuman Khandual <anshuman.khandual@....com>
> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
> Co-developed-by: Mark Rutland <mark.rutland@....com>
> Signed-off-by: Mark Rutland <mark.rutland@....com>
> Tested-by: James Clark <james.clark@...aro.org>
> Signed-off-by: Rob Herring (Arm) <robh@...nel.org>
> ---
> v23:
> - Drop the syscall fixup and directly convert BRBE CALL type to perf
> SYSCALL as only calls to higher EL generate a CALL event
>
> v22:
> - Move branch stack disabling after armpmu_stop() in armpmu_del()
> - Fix branch_records_alloc() to work on heterogeneous systems
> - Make setting .sched_task function ptr conditional on BRBE support
>
> v21:
> - update .sched_task() parameters. task_struct added in v6.15
>
> v20:
> - Fix sparse percpu warning in branch_records_alloc()
> - Use pr_debug instead of pr_debug_once. Add debug print on all error
> cases when event.attr is rejected.
> - Add back some arm64 specific exception types
> - Convert 'call' from user to kernel to syscall as appropriate
> - Drop requiring event and branch privileges to match
> - Only enable exceptions and exception returns if recording kernel
> branches
> - Add "branches" caps sysfs attribute like x86
> - Drop some unused defines
> - Use u64 instead of unsigned long for branch record fields
> - use min() in brbinf_get_cycles()
> - Reword comment about FZP and MDCR_EL2.HPMN interaction
> - Add comments on assumptions about calling brbe_enable()
> - Merge capture_brbe_flags() into perf_entry_from_brbe_regset()
> - Rework BRBE invalidation to avoid invalidating in interrupt handler
> when no handled events capture the branch stack.
> - Also clear BRBCR_ELx in brbe_disable(). This is for KVM nVHE checks
> if BRBE is enabled.
>
> v19:
> - Drop saving of branch records when task scheduled out. (Mark)
> - Got rid of added armpmu ops. All BRBE support contained within pmuv3
> code.
> - Dropped armpmu.num_branch_records as reg_brbidr has same info.
> - Make sched_task() callback actually get called. Enabling requires a
> call to perf_sched_cb_inc().
> - Fix freeze on overflow for VHE
> - The cycle counter doesn't freeze BRBE on overflow, so avoid assigning
> it when BRBE is enabled.
> - Drop all the Arm specific exception branches. Not a clear need for
> them.
> - Simplify enable/disable to avoid RMW and document ISBs needed
> - Fix handling of branch 'cycles' reading. CC field is
> mantissa/exponent, not an integer.
> - Save BRBFCR and BRBCR settings in event->hw.branch_reg.config and
> event->hw.extra_reg.config to avoid recalculating the register value
> each time the event is installed.
> - Rework s/w filtering to better match h/w filtering
> - Reject events with disjoint event filter and branch filter
> - Reject events if exclude_host is set
>
> v18: https://lore.kernel.org/all/20240613061731.3109448-6-anshuman.khandual@arm.com/
> ---
> drivers/perf/Kconfig | 11 +
> drivers/perf/Makefile | 1 +
> drivers/perf/arm_brbe.c | 798 +++++++++++++++++++++++++++++++++++++++++++
> drivers/perf/arm_brbe.h | 47 +++
> drivers/perf/arm_pmu.c | 16 +-
> drivers/perf/arm_pmuv3.c | 125 ++++++-
> include/linux/perf/arm_pmu.h | 8 +
> 7 files changed, 999 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/perf/Kconfig b/drivers/perf/Kconfig
> index 278c929dc87a..a9188dec36fe 100644
> --- a/drivers/perf/Kconfig
> +++ b/drivers/perf/Kconfig
> @@ -223,6 +223,17 @@ config ARM_SPE_PMU
> Extension, which provides periodic sampling of operations in
> the CPU pipeline and reports this via the perf AUX interface.
>
> +config ARM64_BRBE
> + bool "Enable support for branch stack sampling using FEAT_BRBE"
> + depends on ARM_PMUV3 && ARM64
> + default y
> + help
> + Enable perf support for Branch Record Buffer Extension (BRBE) which
> + records all branches taken in an execution path. This supports some
> + branch types and privilege based filtering. It captures additional
> + relevant information such as cycle count, misprediction and branch
> + type, branch privilege level etc.
> +
> config ARM_DMC620_PMU
> tristate "Enable PMU support for the ARM DMC-620 memory controller"
> depends on (ARM64 && ACPI) || COMPILE_TEST
> diff --git a/drivers/perf/Makefile b/drivers/perf/Makefile
> index de71d2574857..192fc8b16204 100644
> --- a/drivers/perf/Makefile
> +++ b/drivers/perf/Makefile
> @@ -23,6 +23,7 @@ obj-$(CONFIG_STARFIVE_STARLINK_PMU) += starfive_starlink_pmu.o
> obj-$(CONFIG_THUNDERX2_PMU) += thunderx2_pmu.o
> obj-$(CONFIG_XGENE_PMU) += xgene_pmu.o
> obj-$(CONFIG_ARM_SPE_PMU) += arm_spe_pmu.o
> +obj-$(CONFIG_ARM64_BRBE) += arm_brbe.o
> obj-$(CONFIG_ARM_DMC620_PMU) += arm_dmc620_pmu.o
> obj-$(CONFIG_MARVELL_CN10K_TAD_PMU) += marvell_cn10k_tad_pmu.o
> obj-$(CONFIG_MARVELL_CN10K_DDR_PMU) += marvell_cn10k_ddr_pmu.o
> diff --git a/drivers/perf/arm_brbe.c b/drivers/perf/arm_brbe.c
> new file mode 100644
> index 000000000000..acdde61a8559
> --- /dev/null
> +++ b/drivers/perf/arm_brbe.c
> @@ -0,0 +1,798 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Branch Record Buffer Extension Driver.
> + *
> + * Copyright (C) 2022-2025 ARM Limited
> + *
> + * Author: Anshuman Khandual <anshuman.khandual@....com>
> + */
> +#include <linux/types.h>
> +#include <linux/bitmap.h>
> +#include <linux/perf/arm_pmu.h>
> +#include "arm_brbe.h"
> +
> +#define BRBFCR_EL1_BRANCH_FILTERS (BRBFCR_EL1_DIRECT | \
> + BRBFCR_EL1_INDIRECT | \
> + BRBFCR_EL1_RTN | \
> + BRBFCR_EL1_INDCALL | \
> + BRBFCR_EL1_DIRCALL | \
> + BRBFCR_EL1_CONDDIR)
> +
> +/*
> + * BRBTS_EL1 is currently not used for branch stack implementation
> + * purpose but BRBCR_ELx.TS needs to have a valid value from all
> + * available options. BRBCR_ELx_TS_VIRTUAL is selected for this.
> + */
> +#define BRBCR_ELx_DEFAULT_TS FIELD_PREP(BRBCR_ELx_TS_MASK, BRBCR_ELx_TS_VIRTUAL)
> +
> +/*
> + * BRBE Buffer Organization
> + *
> + * BRBE buffer is arranged as multiple banks of 32 branch record
> + * entries each. An individual branch record in a given bank could
> + * be accessed, after selecting the bank in BRBFCR_EL1.BANK and
> + * accessing the registers i.e [BRBSRC, BRBTGT, BRBINF] set with
> + * indices [0..31].
> + *
> + * Bank 0
> + *
> + * --------------------------------- ------
> + * | 00 | BRBSRC | BRBTGT | BRBINF | | 00 |
> + * --------------------------------- ------
> + * | 01 | BRBSRC | BRBTGT | BRBINF | | 01 |
> + * --------------------------------- ------
> + * | .. | BRBSRC | BRBTGT | BRBINF | | .. |
> + * --------------------------------- ------
> + * | 31 | BRBSRC | BRBTGT | BRBINF | | 31 |
> + * --------------------------------- ------
> + *
> + * Bank 1
> + *
> + * --------------------------------- ------
> + * | 32 | BRBSRC | BRBTGT | BRBINF | | 00 |
> + * --------------------------------- ------
> + * | 33 | BRBSRC | BRBTGT | BRBINF | | 01 |
> + * --------------------------------- ------
> + * | .. | BRBSRC | BRBTGT | BRBINF | | .. |
> + * --------------------------------- ------
> + * | 63 | BRBSRC | BRBTGT | BRBINF | | 31 |
> + * --------------------------------- ------
> + */
> +#define BRBE_BANK_MAX_ENTRIES 32
> +
> +struct brbe_regset {
> + u64 brbsrc;
> + u64 brbtgt;
> + u64 brbinf;
> +};
> +
> +#define PERF_BR_ARM64_MAX (PERF_BR_MAX + PERF_BR_NEW_MAX)
> +
> +struct brbe_hw_attr {
> + int brbe_version;
> + int brbe_cc;
> + int brbe_nr;
> + int brbe_format;
> +};
> +
> +#define BRBE_REGN_CASE(n, case_macro) \
> + case n: case_macro(n); break
> +
> +#define BRBE_REGN_SWITCH(x, case_macro) \
> + do { \
> + switch (x) { \
> + BRBE_REGN_CASE(0, case_macro); \
> + BRBE_REGN_CASE(1, case_macro); \
> + BRBE_REGN_CASE(2, case_macro); \
> + BRBE_REGN_CASE(3, case_macro); \
> + BRBE_REGN_CASE(4, case_macro); \
> + BRBE_REGN_CASE(5, case_macro); \
> + BRBE_REGN_CASE(6, case_macro); \
> + BRBE_REGN_CASE(7, case_macro); \
> + BRBE_REGN_CASE(8, case_macro); \
> + BRBE_REGN_CASE(9, case_macro); \
> + BRBE_REGN_CASE(10, case_macro); \
> + BRBE_REGN_CASE(11, case_macro); \
> + BRBE_REGN_CASE(12, case_macro); \
> + BRBE_REGN_CASE(13, case_macro); \
> + BRBE_REGN_CASE(14, case_macro); \
> + BRBE_REGN_CASE(15, case_macro); \
> + BRBE_REGN_CASE(16, case_macro); \
> + BRBE_REGN_CASE(17, case_macro); \
> + BRBE_REGN_CASE(18, case_macro); \
> + BRBE_REGN_CASE(19, case_macro); \
> + BRBE_REGN_CASE(20, case_macro); \
> + BRBE_REGN_CASE(21, case_macro); \
> + BRBE_REGN_CASE(22, case_macro); \
> + BRBE_REGN_CASE(23, case_macro); \
> + BRBE_REGN_CASE(24, case_macro); \
> + BRBE_REGN_CASE(25, case_macro); \
> + BRBE_REGN_CASE(26, case_macro); \
> + BRBE_REGN_CASE(27, case_macro); \
> + BRBE_REGN_CASE(28, case_macro); \
> + BRBE_REGN_CASE(29, case_macro); \
> + BRBE_REGN_CASE(30, case_macro); \
> + BRBE_REGN_CASE(31, case_macro); \
> + default: WARN(1, "Invalid BRB* index %d\n", x); \
> + } \
> + } while (0)
> +
> +#define RETURN_READ_BRBSRCN(n) \
> + return read_sysreg_s(SYS_BRBSRC_EL1(n))
> +static inline u64 get_brbsrc_reg(int idx)
> +{
> + BRBE_REGN_SWITCH(idx, RETURN_READ_BRBSRCN);
> + return 0;
> +}
> +
> +#define RETURN_READ_BRBTGTN(n) \
> + return read_sysreg_s(SYS_BRBTGT_EL1(n))
> +static u64 get_brbtgt_reg(int idx)
> +{
> + BRBE_REGN_SWITCH(idx, RETURN_READ_BRBTGTN);
> + return 0;
> +}
> +
> +#define RETURN_READ_BRBINFN(n) \
> + return read_sysreg_s(SYS_BRBINF_EL1(n))
> +static u64 get_brbinf_reg(int idx)
> +{
> + BRBE_REGN_SWITCH(idx, RETURN_READ_BRBINFN);
> + return 0;
> +}
> +
> +static u64 brbe_record_valid(u64 brbinf)
> +{
> + return FIELD_GET(BRBINFx_EL1_VALID_MASK, brbinf);
> +}
> +
> +static bool brbe_invalid(u64 brbinf)
> +{
> + return brbe_record_valid(brbinf) == BRBINFx_EL1_VALID_NONE;
> +}
> +
> +static bool brbe_record_is_complete(u64 brbinf)
> +{
> + return brbe_record_valid(brbinf) == BRBINFx_EL1_VALID_FULL;
> +}
> +
> +static bool brbe_record_is_source_only(u64 brbinf)
> +{
> + return brbe_record_valid(brbinf) == BRBINFx_EL1_VALID_SOURCE;
> +}
> +
> +static bool brbe_record_is_target_only(u64 brbinf)
> +{
> + return brbe_record_valid(brbinf) == BRBINFx_EL1_VALID_TARGET;
> +}
> +
> +static int brbinf_get_in_tx(u64 brbinf)
> +{
> + return FIELD_GET(BRBINFx_EL1_T_MASK, brbinf);
> +}
> +
> +static int brbinf_get_mispredict(u64 brbinf)
> +{
> + return FIELD_GET(BRBINFx_EL1_MPRED_MASK, brbinf);
> +}
> +
> +static int brbinf_get_lastfailed(u64 brbinf)
> +{
> + return FIELD_GET(BRBINFx_EL1_LASTFAILED_MASK, brbinf);
> +}
> +
> +static u16 brbinf_get_cycles(u64 brbinf)
> +{
> + u32 exp, mant, cycles;
> + /*
> + * Captured cycle count is unknown and hence
> + * should not be passed on to userspace.
> + */
> + if (brbinf & BRBINFx_EL1_CCU)
> + return 0;
> +
> + exp = FIELD_GET(BRBINFx_EL1_CC_EXP_MASK, brbinf);
> + mant = FIELD_GET(BRBINFx_EL1_CC_MANT_MASK, brbinf);
> +
> + if (!exp)
> + return mant;
> +
> + cycles = (mant | 0x100) << (exp - 1);
> +
> + return min(cycles, U16_MAX);
> +}
> +
> +static int brbinf_get_type(u64 brbinf)
> +{
> + return FIELD_GET(BRBINFx_EL1_TYPE_MASK, brbinf);
> +}
> +
> +static int brbinf_get_el(u64 brbinf)
> +{
> + return FIELD_GET(BRBINFx_EL1_EL_MASK, brbinf);
> +}
> +
> +void brbe_invalidate(void)
> +{
> + // Ensure all branches before this point are recorded
> + isb();
> + asm volatile(BRB_IALL_INSN);
> + // Ensure all branch records are invalidated after this point
> + isb();
> +}
> +
> +static bool valid_brbe_nr(int brbe_nr)
> +{
> + return brbe_nr == BRBIDR0_EL1_NUMREC_8 ||
> + brbe_nr == BRBIDR0_EL1_NUMREC_16 ||
> + brbe_nr == BRBIDR0_EL1_NUMREC_32 ||
> + brbe_nr == BRBIDR0_EL1_NUMREC_64;
> +}
> +
> +static bool valid_brbe_cc(int brbe_cc)
> +{
> + return brbe_cc == BRBIDR0_EL1_CC_20_BIT;
> +}
> +
> +static bool valid_brbe_format(int brbe_format)
> +{
> + return brbe_format == BRBIDR0_EL1_FORMAT_FORMAT_0;
> +}
> +
> +static bool valid_brbidr(u64 brbidr)
> +{
> + int brbe_format, brbe_cc, brbe_nr;
> +
> + brbe_format = FIELD_GET(BRBIDR0_EL1_FORMAT_MASK, brbidr);
> + brbe_cc = FIELD_GET(BRBIDR0_EL1_CC_MASK, brbidr);
> + brbe_nr = FIELD_GET(BRBIDR0_EL1_NUMREC_MASK, brbidr);
> +
> + return valid_brbe_format(brbe_format) && valid_brbe_cc(brbe_cc) && valid_brbe_nr(brbe_nr);
> +}
> +
> +static bool valid_brbe_version(int brbe_version)
> +{
> + return brbe_version == ID_AA64DFR0_EL1_BRBE_IMP ||
> + brbe_version == ID_AA64DFR0_EL1_BRBE_BRBE_V1P1;
> +}
> +
> +static void select_brbe_bank(int bank)
> +{
> + u64 brbfcr;
> +
> + brbfcr = read_sysreg_s(SYS_BRBFCR_EL1);
> + brbfcr &= ~BRBFCR_EL1_BANK_MASK;
> + brbfcr |= SYS_FIELD_PREP(BRBFCR_EL1, BANK, bank);
> + write_sysreg_s(brbfcr, SYS_BRBFCR_EL1);
> + /*
> + * Arm ARM (DDI 0487K.a) D.18.4 rule PPBZP requires explicit sync
> + * between setting BANK and accessing branch records.
> + */
> + isb();
> +}
> +
> +static bool __read_brbe_regset(struct brbe_regset *entry, int idx)
> +{
> + entry->brbinf = get_brbinf_reg(idx);
> +
> + if (brbe_invalid(entry->brbinf))
> + return false;
> +
> + entry->brbsrc = get_brbsrc_reg(idx);
> + entry->brbtgt = get_brbtgt_reg(idx);
> + return true;
> +}
> +
> +/*
> + * Generic perf branch filters supported on BRBE
> + *
> + * New branch filters need to be evaluated whether they could be supported on
> + * BRBE. This ensures that such branch filters would not just be accepted, to
> + * fail silently. PERF_SAMPLE_BRANCH_HV is a special case that is selectively
> + * supported only on platforms where kernel is in hyp mode.
> + */
> +#define BRBE_EXCLUDE_BRANCH_FILTERS (PERF_SAMPLE_BRANCH_ABORT_TX | \
> + PERF_SAMPLE_BRANCH_IN_TX | \
> + PERF_SAMPLE_BRANCH_NO_TX | \
> + PERF_SAMPLE_BRANCH_CALL_STACK | \
> + PERF_SAMPLE_BRANCH_COUNTERS)
> +
> +#define BRBE_ALLOWED_BRANCH_TYPES (PERF_SAMPLE_BRANCH_ANY | \
> + PERF_SAMPLE_BRANCH_ANY_CALL | \
> + PERF_SAMPLE_BRANCH_ANY_RETURN | \
> + PERF_SAMPLE_BRANCH_IND_CALL | \
> + PERF_SAMPLE_BRANCH_COND | \
> + PERF_SAMPLE_BRANCH_IND_JUMP | \
> + PERF_SAMPLE_BRANCH_CALL)
> +
> +
> +#define BRBE_ALLOWED_BRANCH_FILTERS (PERF_SAMPLE_BRANCH_USER | \
> + PERF_SAMPLE_BRANCH_KERNEL | \
> + PERF_SAMPLE_BRANCH_HV | \
> + BRBE_ALLOWED_BRANCH_TYPES | \
> + PERF_SAMPLE_BRANCH_NO_FLAGS | \
> + PERF_SAMPLE_BRANCH_NO_CYCLES | \
> + PERF_SAMPLE_BRANCH_TYPE_SAVE | \
> + PERF_SAMPLE_BRANCH_HW_INDEX | \
> + PERF_SAMPLE_BRANCH_PRIV_SAVE)
> +
> +#define BRBE_PERF_BRANCH_FILTERS (BRBE_ALLOWED_BRANCH_FILTERS | \
> + BRBE_EXCLUDE_BRANCH_FILTERS)
> +
> +/*
> + * BRBE supports the following functional branch type filters while
> + * generating branch records. These branch filters can be enabled,
> + * either individually or as a group i.e ORing multiple filters
> + * with each other.
> + *
> + * BRBFCR_EL1_CONDDIR - Conditional direct branch
> + * BRBFCR_EL1_DIRCALL - Direct call
> + * BRBFCR_EL1_INDCALL - Indirect call
> + * BRBFCR_EL1_INDIRECT - Indirect branch
> + * BRBFCR_EL1_DIRECT - Direct branch
> + * BRBFCR_EL1_RTN - Subroutine return
> + */
> +static u64 branch_type_to_brbfcr(int branch_type)
> +{
> + u64 brbfcr = 0;
> +
> + if (branch_type & PERF_SAMPLE_BRANCH_ANY) {
> + brbfcr |= BRBFCR_EL1_BRANCH_FILTERS;
> + return brbfcr;
> + }
> +
> + if (branch_type & PERF_SAMPLE_BRANCH_ANY_CALL) {
> + brbfcr |= BRBFCR_EL1_INDCALL;
> + brbfcr |= BRBFCR_EL1_DIRCALL;
> + }
> +
> + if (branch_type & PERF_SAMPLE_BRANCH_ANY_RETURN)
> + brbfcr |= BRBFCR_EL1_RTN;
> +
> + if (branch_type & PERF_SAMPLE_BRANCH_IND_CALL)
> + brbfcr |= BRBFCR_EL1_INDCALL;
> +
> + if (branch_type & PERF_SAMPLE_BRANCH_COND)
> + brbfcr |= BRBFCR_EL1_CONDDIR;
> +
> + if (branch_type & PERF_SAMPLE_BRANCH_IND_JUMP)
> + brbfcr |= BRBFCR_EL1_INDIRECT;
> +
> + if (branch_type & PERF_SAMPLE_BRANCH_CALL)
> + brbfcr |= BRBFCR_EL1_DIRCALL;
> +
> + return brbfcr;
> +}
> +
> +/*
> + * BRBE supports the following privilege mode filters while generating
> + * branch records.
> + *
> + * BRBCR_ELx_E0BRE - EL0 branch records
> + * BRBCR_ELx_ExBRE - EL1/EL2 branch records
> + *
> + * BRBE also supports the following additional functional branch type
> + * filters while generating branch records.
> + *
> + * BRBCR_ELx_EXCEPTION - Exception
> + * BRBCR_ELx_ERTN - Exception return
> + */
> +static u64 branch_type_to_brbcr(int branch_type)
> +{
> + u64 brbcr = BRBCR_ELx_FZP | BRBCR_ELx_DEFAULT_TS;
> +
> + if (branch_type & PERF_SAMPLE_BRANCH_USER)
> + brbcr |= BRBCR_ELx_E0BRE;
> +
> + /*
> + * When running in the hyp mode, writing into BRBCR_EL1
> + * actually writes into BRBCR_EL2 instead. Field E2BRE
> + * is also at the same position as E1BRE.
> + */
> + if (branch_type & PERF_SAMPLE_BRANCH_KERNEL)
> + brbcr |= BRBCR_ELx_ExBRE;
> +
> + if (branch_type & PERF_SAMPLE_BRANCH_HV) {
> + if (is_kernel_in_hyp_mode())
> + brbcr |= BRBCR_ELx_ExBRE;
> + }
> +
> + if (!(branch_type & PERF_SAMPLE_BRANCH_NO_CYCLES))
> + brbcr |= BRBCR_ELx_CC;
> +
> + if (!(branch_type & PERF_SAMPLE_BRANCH_NO_FLAGS))
> + brbcr |= BRBCR_ELx_MPRED;
> +
> + /*
> + * The exception and exception return branches could be
> + * captured, irrespective of the perf event's privilege.
> + * If the perf event does not have enough privilege for
> + * a given exception level, then addresses which falls
> + * under that exception level will be reported as zero
> + * for the captured branch record, creating source only
> + * or target only records.
> + */
> + if (branch_type & PERF_SAMPLE_BRANCH_KERNEL) {
> + if (branch_type & PERF_SAMPLE_BRANCH_ANY) {
> + brbcr |= BRBCR_ELx_EXCEPTION;
> + brbcr |= BRBCR_ELx_ERTN;
> + }
> +
> + if (branch_type & PERF_SAMPLE_BRANCH_ANY_CALL)
> + brbcr |= BRBCR_ELx_EXCEPTION;
> +
> + if (branch_type & PERF_SAMPLE_BRANCH_ANY_RETURN)
> + brbcr |= BRBCR_ELx_ERTN;
> + }
> + return brbcr;
> +}
> +
> +bool brbe_branch_attr_valid(struct perf_event *event)
> +{
> + u64 branch_type = event->attr.branch_sample_type;
> +
> + /*
> + * Ensure both perf branch filter allowed and exclude
> + * masks are always in sync with the generic perf ABI.
> + */
> + BUILD_BUG_ON(BRBE_PERF_BRANCH_FILTERS != (PERF_SAMPLE_BRANCH_MAX - 1));
> +
> + if (branch_type & BRBE_EXCLUDE_BRANCH_FILTERS) {
> + pr_debug("requested branch filter not supported 0x%llx\n", branch_type);
> + return false;
> + }
> +
> + /* Ensure at least 1 branch type is enabled */
> + if (!(branch_type & BRBE_ALLOWED_BRANCH_TYPES)) {
> + pr_debug("no branch type enabled 0x%llx\n", branch_type);
> + return false;
> + }
> +
> + /*
> + * No branches are recorded in guests nor nVHE hypervisors, so
> + * excluding the host or both kernel and user is invalid.
> + *
> + * Ideally we'd just require exclude_guest and exclude_hv, but setting
> + * event filters with perf for kernel or user don't set exclude_guest.
> + * So effectively, exclude_guest and exclude_hv are ignored.
> + */
> + if (event->attr.exclude_host || (event->attr.exclude_user && event->attr.exclude_kernel)) {
> + pr_debug("branch filter in hypervisor or guest only not supported 0x%llx\n", branch_type);
> + return false;
> + }
> +
> + event->hw.branch_reg.config = branch_type_to_brbfcr(event->attr.branch_sample_type);
> + event->hw.extra_reg.config = branch_type_to_brbcr(event->attr.branch_sample_type);
> +
> + return true;
> +}
> +
> +unsigned int brbe_num_branch_records(const struct arm_pmu *armpmu)
> +{
> + return FIELD_GET(BRBIDR0_EL1_NUMREC_MASK, armpmu->reg_brbidr);
> +}
> +
> +void brbe_probe(struct arm_pmu *armpmu)
> +{
> + u64 aa64dfr0 = read_sysreg_s(SYS_ID_AA64DFR0_EL1);
> + u32 brbe;
> +
> + brbe = cpuid_feature_extract_unsigned_field(aa64dfr0, ID_AA64DFR0_EL1_BRBE_SHIFT);
> + if (!valid_brbe_version(brbe))
> + return;
> +
> + u64 brbidr = read_sysreg_s(SYS_BRBIDR0_EL1);
> + if (!valid_brbidr(brbidr))
> + return;
> +
> + armpmu->reg_brbidr = brbidr;
> +}
> +
> +/*
> + * BRBE is assumed to be disabled/paused on entry
> + */
> +void brbe_enable(const struct arm_pmu *arm_pmu)
> +{
> + struct pmu_hw_events *cpuc = this_cpu_ptr(arm_pmu->hw_events);
> + u64 brbfcr = 0, brbcr = 0;
> +
> + /*
> + * Merge the permitted branch filters of all events.
> + */
> + for (int i = 0; i < ARMPMU_MAX_HWEVENTS; i++) {
> + struct perf_event *event = cpuc->events[i];
> +
> + if (event && has_branch_stack(event)) {
> + brbfcr |= event->hw.branch_reg.config;
> + brbcr |= event->hw.extra_reg.config;
> + }
> + }
> +
> + /*
> + * In VHE mode with MDCR_EL2.HPMN equal to PMCR_EL0.N, BRBCR_EL1.FZP
> + * controls freezing the branch records on counter overflow rather than
> + * BRBCR_EL2.FZP (which writes to BRBCR_EL1 are redirected to).
> + * The exception levels are enabled/disabled in BRBCR_EL2, so keep EL1
> + * and EL0 recording disabled for guests.
> + *
> + * As BRBCR_EL1 CC and MPRED bits also need to match, use the same
> + * value for both registers just masking the exception levels.
> + */
> + if (is_kernel_in_hyp_mode())
> + write_sysreg_s(brbcr & ~(BRBCR_ELx_ExBRE | BRBCR_ELx_E0BRE), SYS_BRBCR_EL12);
> + write_sysreg_s(brbcr, SYS_BRBCR_EL1);
> + isb(); // Ensure BRBCR_ELx settings take effect before unpausing
> +
> + // Finally write SYS_BRBFCR_EL to unpause BRBE
> + write_sysreg_s(brbfcr, SYS_BRBFCR_EL1);
> + // Synchronization in PMCR write ensures ordering WRT PMU enabling
> +}
> +
> +void brbe_disable(void)
> +{
> + /*
> + * No need for synchronization here as synchronization in PMCR write
> + * ensures ordering and in the interrupt handler this is a NOP as
> + * we're already paused.
> + */
> + write_sysreg_s(BRBFCR_EL1_PAUSED, SYS_BRBFCR_EL1);
> + write_sysreg_s(0, SYS_BRBCR_EL1);
> +}
> +
> +static const int brbe_type_to_perf_type_map[BRBINFx_EL1_TYPE_DEBUG_EXIT + 1][2] = {
> + [BRBINFx_EL1_TYPE_DIRECT_UNCOND] = { PERF_BR_UNCOND, 0 },
> + [BRBINFx_EL1_TYPE_INDIRECT] = { PERF_BR_IND, 0 },
> + [BRBINFx_EL1_TYPE_DIRECT_LINK] = { PERF_BR_CALL, 0 },
> + [BRBINFx_EL1_TYPE_INDIRECT_LINK] = { PERF_BR_IND_CALL, 0 },
> + [BRBINFx_EL1_TYPE_RET] = { PERF_BR_RET, 0 },
> + [BRBINFx_EL1_TYPE_DIRECT_COND] = { PERF_BR_COND, 0 },
> + [BRBINFx_EL1_TYPE_CALL] = { PERF_BR_SYSCALL, 0 },
> + [BRBINFx_EL1_TYPE_ERET] = { PERF_BR_ERET, 0 },
> + [BRBINFx_EL1_TYPE_IRQ] = { PERF_BR_IRQ, 0 },
> + [BRBINFx_EL1_TYPE_TRAP] = { PERF_BR_IRQ, 0 },
> + [BRBINFx_EL1_TYPE_SERROR] = { PERF_BR_SERROR, 0 },
> + [BRBINFx_EL1_TYPE_ALIGN_FAULT] = { PERF_BR_EXTEND_ABI, PERF_BR_NEW_FAULT_ALGN },
> + [BRBINFx_EL1_TYPE_INSN_FAULT] = { PERF_BR_EXTEND_ABI, PERF_BR_NEW_FAULT_INST },
> + [BRBINFx_EL1_TYPE_DATA_FAULT] = { PERF_BR_EXTEND_ABI, PERF_BR_NEW_FAULT_DATA },
> +};
> +
> +static void brbe_set_perf_entry_type(struct perf_branch_entry *entry, u64 brbinf)
> +{
> + int brbe_type = brbinf_get_type(brbinf);
> +
> + if (brbe_type <= BRBINFx_EL1_TYPE_DEBUG_EXIT) {
> + const int *br_type = brbe_type_to_perf_type_map[brbe_type];
> +
> + entry->type = br_type[0];
> + entry->new_type = br_type[1];
> + }
> +}
> +
> +static int brbinf_get_perf_priv(u64 brbinf)
> +{
> + int brbe_el = brbinf_get_el(brbinf);
> +
> + switch (brbe_el) {
> + case BRBINFx_EL1_EL_EL0:
> + return PERF_BR_PRIV_USER;
> + case BRBINFx_EL1_EL_EL1:
> + return PERF_BR_PRIV_KERNEL;
> + case BRBINFx_EL1_EL_EL2:
> + if (is_kernel_in_hyp_mode())
> + return PERF_BR_PRIV_KERNEL;
> + return PERF_BR_PRIV_HV;
> + default:
> + pr_warn_once("%d - unknown branch privilege captured\n", brbe_el);
> + return PERF_BR_PRIV_UNKNOWN;
> + }
> +}
> +
> +static bool perf_entry_from_brbe_regset(int index, struct perf_branch_entry *entry,
> + const struct perf_event *event)
> +{
> + struct brbe_regset bregs;
> + u64 brbinf;
> +
> + if (!__read_brbe_regset(&bregs, index))
> + return false;
> +
> + brbinf = bregs.brbinf;
> + perf_clear_branch_entry_bitfields(entry);
> + if (brbe_record_is_complete(brbinf)) {
> + entry->from = bregs.brbsrc;
> + entry->to = bregs.brbtgt;
> + } else if (brbe_record_is_source_only(brbinf)) {
> + entry->from = bregs.brbsrc;
> + entry->to = 0;
> + } else if (brbe_record_is_target_only(brbinf)) {
> + entry->from = 0;
> + entry->to = bregs.brbtgt;
> + }
> +
> + brbe_set_perf_entry_type(entry, brbinf);
> +
> + if (!branch_sample_no_cycles(event))
> + entry->cycles = brbinf_get_cycles(brbinf);
> +
> + if (!branch_sample_no_flags(event)) {
> + /* Mispredict info is available for source only and complete branch records. */
> + if (!brbe_record_is_target_only(brbinf)) {
> + entry->mispred = brbinf_get_mispredict(brbinf);
> + entry->predicted = !entry->mispred;
> + }
> +
> + /*
> + * Currently TME feature is neither implemented in any hardware
> + * nor it is being supported in the kernel. Just warn here once
> + * if TME related information shows up rather unexpectedly.
> + */
> + if (brbinf_get_lastfailed(brbinf) || brbinf_get_in_tx(brbinf))
> + pr_warn_once("Unknown transaction states\n");
> + }
> +
> + /*
> + * Branch privilege level is available for target only and complete
> + * branch records.
> + */
> + if (!brbe_record_is_source_only(brbinf))
> + entry->priv = brbinf_get_perf_priv(brbinf);
> +
> + return true;
> +}
> +
> +#define PERF_BR_ARM64_ALL ( \
> + BIT(PERF_BR_COND) | \
> + BIT(PERF_BR_UNCOND) | \
> + BIT(PERF_BR_IND) | \
> + BIT(PERF_BR_CALL) | \
> + BIT(PERF_BR_IND_CALL) | \
> + BIT(PERF_BR_RET))
> +
> +#define PERF_BR_ARM64_ALL_KERNEL ( \
> + BIT(PERF_BR_SYSCALL) | \
> + BIT(PERF_BR_IRQ) | \
> + BIT(PERF_BR_SERROR) | \
> + BIT(PERF_BR_MAX + PERF_BR_NEW_FAULT_ALGN) | \
> + BIT(PERF_BR_MAX + PERF_BR_NEW_FAULT_DATA) | \
> + BIT(PERF_BR_MAX + PERF_BR_NEW_FAULT_INST))
> +
> +static void prepare_event_branch_type_mask(u64 branch_sample,
> + unsigned long *event_type_mask)
> +{
> + if (branch_sample & PERF_SAMPLE_BRANCH_ANY) {
> + if (branch_sample & PERF_SAMPLE_BRANCH_KERNEL)
> + bitmap_from_u64(event_type_mask,
> + BIT(PERF_BR_ERET) | PERF_BR_ARM64_ALL |
> + PERF_BR_ARM64_ALL_KERNEL);
> + else
> + bitmap_from_u64(event_type_mask, PERF_BR_ARM64_ALL);
> + return;
> + }
> +
> + bitmap_zero(event_type_mask, PERF_BR_ARM64_MAX);
> +
> + if (branch_sample & PERF_SAMPLE_BRANCH_ANY_CALL) {
> + if (branch_sample & PERF_SAMPLE_BRANCH_KERNEL)
> + bitmap_from_u64(event_type_mask, PERF_BR_ARM64_ALL_KERNEL);
> +
> + set_bit(PERF_BR_CALL, event_type_mask);
> + set_bit(PERF_BR_IND_CALL, event_type_mask);
> + }
> +
> + if (branch_sample & PERF_SAMPLE_BRANCH_IND_JUMP)
> + set_bit(PERF_BR_IND, event_type_mask);
> +
> + if (branch_sample & PERF_SAMPLE_BRANCH_COND)
> + set_bit(PERF_BR_COND, event_type_mask);
> +
> + if (branch_sample & PERF_SAMPLE_BRANCH_CALL)
> + set_bit(PERF_BR_CALL, event_type_mask);
> +
> + if (branch_sample & PERF_SAMPLE_BRANCH_IND_CALL)
> + set_bit(PERF_BR_IND_CALL, event_type_mask);
> +
> + if (branch_sample & PERF_SAMPLE_BRANCH_ANY_RETURN) {
> + set_bit(PERF_BR_RET, event_type_mask);
> +
> + if (branch_sample & PERF_SAMPLE_BRANCH_KERNEL)
> + set_bit(PERF_BR_ERET, event_type_mask);
> + }
> +}
> +
> +/*
> + * BRBE is configured with an OR of permissions from all events, so there may
> + * be events which have to be dropped or events where just the source or target
> + * address has to be zeroed.
> + */
> +static bool filter_branch_privilege(struct perf_branch_entry *entry, u64 branch_sample_type)
> +{
> + /* We can only have a half record if permissions have not been expanded */
> + if (!entry->from || !entry->to)
> + return true;
> +
> + bool from_user = access_ok((void __user *)(unsigned long)entry->from, 4);
> + bool to_user = access_ok((void __user *)(unsigned long)entry->to, 4);
> + bool exclude_kernel = !((branch_sample_type & PERF_SAMPLE_BRANCH_KERNEL) ||
> + (is_kernel_in_hyp_mode() && (branch_sample_type & PERF_SAMPLE_BRANCH_HV)));
> +
> + /*
> + * If record is within a single exception level, just need to either
> + * drop or keep the entire record.
> + */
> + if (from_user == to_user)
> + return ((entry->priv == PERF_BR_PRIV_KERNEL) && !exclude_kernel) ||
> + ((entry->priv == PERF_BR_PRIV_USER) &&
> + (branch_sample_type & PERF_SAMPLE_BRANCH_USER));
> +
> + /*
> + * Record is across exception levels, mask addresses for the exception
> + * level we're not capturing.
> + */
> + if (!(branch_sample_type & PERF_SAMPLE_BRANCH_USER)) {
> + if (from_user)
> + entry->from = 0;
> + if (to_user)
> + entry->to = 0;
> + }
> +
> + if (exclude_kernel) {
> + if (!from_user)
> + entry->from = 0;
> + if (!to_user)
> + entry->to = 0;
> + }
> + return true;
> +}
> +
> +static bool filter_branch_type(struct perf_branch_entry *entry,
> + const unsigned long *event_type_mask)
> +{
> + if (entry->type == PERF_BR_EXTEND_ABI)
> + return test_bit(PERF_BR_MAX + entry->new_type, event_type_mask);
> + else
> + return test_bit(entry->type, event_type_mask);
> +}
> +
> +static bool filter_branch_record(struct perf_branch_entry *entry,
> + u64 branch_sample,
> + const unsigned long *event_type_mask)
> +{
> + return filter_branch_type(entry, event_type_mask) &&
> + filter_branch_privilege(entry, branch_sample);
> +}
> +
> +void brbe_read_filtered_entries(struct perf_branch_stack *branch_stack,
> + const struct perf_event *event)
> +{
> + struct arm_pmu *cpu_pmu = to_arm_pmu(event->pmu);
> + int nr_hw = brbe_num_branch_records(cpu_pmu);
> + int nr_banks = DIV_ROUND_UP(nr_hw, BRBE_BANK_MAX_ENTRIES);
> + int nr_filtered = 0;
> + u64 branch_sample_type = event->attr.branch_sample_type;
> + DECLARE_BITMAP(event_type_mask, PERF_BR_ARM64_MAX);
> +
> + prepare_event_branch_type_mask(branch_sample_type, event_type_mask);
> +
> + for (int bank = 0; bank < nr_banks; bank++) {
> + int nr_remaining = nr_hw - (bank * BRBE_BANK_MAX_ENTRIES);
> + int nr_this_bank = min(nr_remaining, BRBE_BANK_MAX_ENTRIES);
> +
> + select_brbe_bank(bank);
> +
> + for (int i = 0; i < nr_this_bank; i++) {
> + struct perf_branch_entry *pbe = &branch_stack->entries[nr_filtered];
> +
> + if (!perf_entry_from_brbe_regset(i, pbe, event))
> + goto done;
> +
> + if (!filter_branch_record(pbe, branch_sample_type, event_type_mask))
> + continue;
> +
> + nr_filtered++;
> + }
> + }
> +
> +done:
> + brbe_invalidate();
> + branch_stack->nr = nr_filtered;
> +}
> diff --git a/drivers/perf/arm_brbe.h b/drivers/perf/arm_brbe.h
> new file mode 100644
> index 000000000000..b7c7d8796c86
> --- /dev/null
> +++ b/drivers/perf/arm_brbe.h
> @@ -0,0 +1,47 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Branch Record Buffer Extension Helpers.
> + *
> + * Copyright (C) 2022-2025 ARM Limited
> + *
> + * Author: Anshuman Khandual <anshuman.khandual@....com>
> + */
> +
> +struct arm_pmu;
> +struct perf_branch_stack;
> +struct perf_event;
> +
> +#ifdef CONFIG_ARM64_BRBE
> +void brbe_probe(struct arm_pmu *arm_pmu);
> +unsigned int brbe_num_branch_records(const struct arm_pmu *armpmu);
> +void brbe_invalidate(void);
> +
> +void brbe_enable(const struct arm_pmu *arm_pmu);
> +void brbe_disable(void);
> +
> +bool brbe_branch_attr_valid(struct perf_event *event);
> +void brbe_read_filtered_entries(struct perf_branch_stack *branch_stack,
> + const struct perf_event *event);
> +#else
> +static inline void brbe_probe(struct arm_pmu *arm_pmu) { }
> +static inline unsigned int brbe_num_branch_records(const struct arm_pmu *armpmu)
> +{
> + return 0;
> +}
> +
> +static inline void brbe_invalidate(void) { }
> +
> +static inline void brbe_enable(const struct arm_pmu *arm_pmu) { };
> +static inline void brbe_disable(void) { };
> +
> +static inline bool brbe_branch_attr_valid(struct perf_event *event)
> +{
> + WARN_ON_ONCE(!has_branch_stack(event));
> + return false;
> +}
> +
> +static void brbe_read_filtered_entries(struct perf_branch_stack *branch_stack,
> + const struct perf_event *event)
> +{
> +}
> +#endif
> diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c
> index 2f33e69a8caf..5c310e803dd7 100644
> --- a/drivers/perf/arm_pmu.c
> +++ b/drivers/perf/arm_pmu.c
> @@ -99,7 +99,7 @@ static const struct pmu_irq_ops percpu_pmunmi_ops = {
> .free_pmuirq = armpmu_free_percpu_pmunmi
> };
>
> -static DEFINE_PER_CPU(struct arm_pmu *, cpu_armpmu);
> +DEFINE_PER_CPU(struct arm_pmu *, cpu_armpmu);
> static DEFINE_PER_CPU(int, cpu_irq);
> static DEFINE_PER_CPU(const struct pmu_irq_ops *, cpu_irq_ops);
>
> @@ -318,6 +318,12 @@ armpmu_del(struct perf_event *event, int flags)
> int idx = hwc->idx;
>
> armpmu_stop(event, PERF_EF_UPDATE);
> +
> + if (has_branch_stack(event)) {
> + hw_events->branch_users--;
> + perf_sched_cb_dec(event->pmu);
> + }
> +
> hw_events->events[idx] = NULL;
> armpmu->clear_event_idx(hw_events, event);
> perf_event_update_userpage(event);
> @@ -345,6 +351,11 @@ armpmu_add(struct perf_event *event, int flags)
> /* The newly-allocated counter should be empty */
> WARN_ON_ONCE(hw_events->events[idx]);
>
> + if (has_branch_stack(event)) {
> + hw_events->branch_users++;
> + perf_sched_cb_inc(event->pmu);
> + }
> +
> event->hw.idx = idx;
> hw_events->events[idx] = event;
>
> @@ -509,8 +520,7 @@ static int armpmu_event_init(struct perf_event *event)
> !cpumask_test_cpu(event->cpu, &armpmu->supported_cpus))
> return -ENOENT;
>
> - /* does not support taken branch sampling */
> - if (has_branch_stack(event))
> + if (has_branch_stack(event) && !armpmu->reg_brbidr)
> return -EOPNOTSUPP;
>
> return __hw_perf_event_init(event);
> diff --git a/drivers/perf/arm_pmuv3.c b/drivers/perf/arm_pmuv3.c
> index 3db9f4ed17e8..256c5ee8709c 100644
> --- a/drivers/perf/arm_pmuv3.c
> +++ b/drivers/perf/arm_pmuv3.c
> @@ -25,6 +25,8 @@
> #include <linux/smp.h>
> #include <linux/nmi.h>
>
> +#include "arm_brbe.h"
> +
> /* ARMv8 Cortex-A53 specific event types. */
> #define ARMV8_A53_PERFCTR_PREF_LINEFILL 0xC2
>
> @@ -438,7 +440,19 @@ static ssize_t threshold_max_show(struct device *dev,
>
> static DEVICE_ATTR_RO(threshold_max);
>
> +static ssize_t branches_show(struct device *dev,
> + struct device_attribute *attr, char *page)
> +{
> + struct pmu *pmu = dev_get_drvdata(dev);
> + struct arm_pmu *cpu_pmu = container_of(pmu, struct arm_pmu, pmu);
> +
> + return sysfs_emit(page, "%d\n", brbe_num_branch_records(cpu_pmu));
> +}
> +
> +static DEVICE_ATTR_RO(branches);
> +
> static struct attribute *armv8_pmuv3_caps_attrs[] = {
> + &dev_attr_branches.attr,
> &dev_attr_slots.attr,
> &dev_attr_bus_slots.attr,
> &dev_attr_bus_width.attr,
> @@ -446,9 +460,22 @@ static struct attribute *armv8_pmuv3_caps_attrs[] = {
> NULL,
> };
>
> +static umode_t caps_is_visible(struct kobject *kobj, struct attribute *attr, int i)
> +{
> + struct device *dev = kobj_to_dev(kobj);
> + struct pmu *pmu = dev_get_drvdata(dev);
> + struct arm_pmu *cpu_pmu = container_of(pmu, struct arm_pmu, pmu);
> +
> + if (i == 0)
> + return brbe_num_branch_records(cpu_pmu) ? attr->mode : 0;
> +
> + return attr->mode;
> +}
> +
> static const struct attribute_group armv8_pmuv3_caps_attr_group = {
> .name = "caps",
> .attrs = armv8_pmuv3_caps_attrs,
> + .is_visible = caps_is_visible,
> };
>
> /*
> @@ -806,9 +833,10 @@ static void armv8pmu_disable_event(struct perf_event *event)
> armv8pmu_disable_event_irq(event);
> }
>
> -static void armv8pmu_start(struct arm_pmu *cpu_pmu)
> +static void armv8pmu_restart(struct arm_pmu *cpu_pmu)
> {
> struct perf_event_context *ctx;
> + struct pmu_hw_events *hw_events = this_cpu_ptr(cpu_pmu->hw_events);
> int nr_user = 0;
>
> ctx = perf_cpu_task_ctx();
> @@ -822,16 +850,44 @@ static void armv8pmu_start(struct arm_pmu *cpu_pmu)
>
> kvm_vcpu_pmu_resync_el0();
>
> + if (hw_events->branch_users)
> + brbe_enable(cpu_pmu);
> +
> /* Enable all counters */
> armv8pmu_pmcr_write(armv8pmu_pmcr_read() | ARMV8_PMU_PMCR_E);
> }
>
> +static void armv8pmu_start(struct arm_pmu *cpu_pmu)
> +{
> + struct pmu_hw_events *hw_events = this_cpu_ptr(cpu_pmu->hw_events);
> +
> + if (hw_events->branch_users)
> + brbe_invalidate();
> +
> + armv8pmu_restart(cpu_pmu);
> +}
> +
> static void armv8pmu_stop(struct arm_pmu *cpu_pmu)
> {
> + struct pmu_hw_events *hw_events = this_cpu_ptr(cpu_pmu->hw_events);
> +
> + if (hw_events->branch_users)
> + brbe_disable();
> +
> /* Disable all counters */
> armv8pmu_pmcr_write(armv8pmu_pmcr_read() & ~ARMV8_PMU_PMCR_E);
> }
>
> +static void read_branch_records(struct pmu_hw_events *cpuc,
> + struct perf_event *event,
> + struct perf_sample_data *data)
> +{
> + struct perf_branch_stack *branch_stack = cpuc->branch_stack;
> +
> + brbe_read_filtered_entries(branch_stack, event);
> + perf_sample_save_brstack(data, event, branch_stack, NULL);
> +}
> +
> static irqreturn_t armv8pmu_handle_irq(struct arm_pmu *cpu_pmu)
> {
> u64 pmovsr;
> @@ -882,6 +938,13 @@ static irqreturn_t armv8pmu_handle_irq(struct arm_pmu *cpu_pmu)
> if (!armpmu_event_set_period(event))
> continue;
>
> + /*
> + * PMU IRQ should remain asserted until all branch records
> + * are captured and processed into struct perf_sample_data.
> + */
> + if (has_branch_stack(event))
> + read_branch_records(cpuc, event, &data);
> +
> /*
> * Perf event overflow will queue the processing of the event as
> * an irq_work which will be taken care of in the handling of
> @@ -889,7 +952,7 @@ static irqreturn_t armv8pmu_handle_irq(struct arm_pmu *cpu_pmu)
> */
> perf_event_overflow(event, &data, regs);
> }
> - armv8pmu_start(cpu_pmu);
> + armv8pmu_restart(cpu_pmu);
>
> return IRQ_HANDLED;
> }
> @@ -938,7 +1001,7 @@ static int armv8pmu_get_event_idx(struct pmu_hw_events *cpuc,
>
> /* Always prefer to place a cycle counter into the cycle counter. */
> if ((evtype == ARMV8_PMUV3_PERFCTR_CPU_CYCLES) &&
> - !armv8pmu_event_get_threshold(&event->attr)) {
> + !armv8pmu_event_get_threshold(&event->attr) && !has_branch_stack(event)) {
> if (!test_and_set_bit(ARMV8_PMU_CYCLE_IDX, cpuc->used_mask))
> return ARMV8_PMU_CYCLE_IDX;
> else if (armv8pmu_event_is_64bit(event) &&
> @@ -987,6 +1050,19 @@ static int armv8pmu_user_event_idx(struct perf_event *event)
> return event->hw.idx + 1;
> }
>
> +static void armv8pmu_sched_task(struct perf_event_pmu_context *pmu_ctx,
> + struct task_struct *task, bool sched_in)
> +{
> + struct arm_pmu *armpmu = *this_cpu_ptr(&cpu_armpmu);
> + struct pmu_hw_events *hw_events = this_cpu_ptr(armpmu->hw_events);
> +
> + if (!hw_events->branch_users)
> + return;
> +
> + if (sched_in)
> + brbe_invalidate();
> +}
> +
> /*
> * Add an event filter to a given event.
> */
> @@ -1004,6 +1080,13 @@ static int armv8pmu_set_event_filter(struct hw_perf_event *event,
> return -EOPNOTSUPP;
> }
>
> + if (has_branch_stack(perf_event)) {
> + if (!brbe_num_branch_records(cpu_pmu) || !brbe_branch_attr_valid(perf_event))
> + return -EOPNOTSUPP;
> +
> + perf_event->attach_state |= PERF_ATTACH_SCHED_CB;
> + }
> +
> /*
> * If we're running in hyp mode, then we *are* the hypervisor.
> * Therefore we ignore exclude_hv in this configuration, since
> @@ -1070,6 +1153,11 @@ static void armv8pmu_reset(void *info)
> /* Clear the counters we flip at guest entry/exit */
> kvm_clr_pmu_events(mask);
>
> + if (brbe_num_branch_records(cpu_pmu)) {
> + brbe_disable();
> + brbe_invalidate();
> + }
> +
> /*
> * Initialize & Reset PMNC. Request overflow interrupt for
> * 64 bit cycle counter but cheat in armv8pmu_write_counter().
> @@ -1238,6 +1326,25 @@ static void __armv8pmu_probe_pmu(void *info)
> cpu_pmu->reg_pmmir = read_pmmir();
> else
> cpu_pmu->reg_pmmir = 0;
> +
> + brbe_probe(cpu_pmu);
> +}
> +
> +static int branch_records_alloc(struct arm_pmu *armpmu)
> +{
> + size_t size = struct_size_t(struct perf_branch_stack, entries,
> + brbe_num_branch_records(armpmu));
> + int cpu;
> +
> + for_each_cpu(cpu, &armpmu->supported_cpus) {
> + struct pmu_hw_events *events_cpu;
> +
> + events_cpu = per_cpu_ptr(armpmu->hw_events, cpu);
> + events_cpu->branch_stack = kmalloc(size, GFP_KERNEL);
> + if (!events_cpu->branch_stack)
> + return -ENOMEM;
> + }
> + return 0;
> }
>
> static int armv8pmu_probe_pmu(struct arm_pmu *cpu_pmu)
> @@ -1254,7 +1361,15 @@ static int armv8pmu_probe_pmu(struct arm_pmu *cpu_pmu)
> if (ret)
> return ret;
>
> - return probe.present ? 0 : -ENODEV;
> + if (!probe.present)
> + return -ENODEV;
> +
> + if (brbe_num_branch_records(cpu_pmu)) {
> + ret = branch_records_alloc(cpu_pmu);
> + if (ret)
> + return ret;
> + }
> + return 0;
> }
>
> static void armv8pmu_disable_user_access_ipi(void *unused)
> @@ -1313,6 +1428,8 @@ static int armv8_pmu_init(struct arm_pmu *cpu_pmu, char *name,
> cpu_pmu->set_event_filter = armv8pmu_set_event_filter;
>
> cpu_pmu->pmu.event_idx = armv8pmu_user_event_idx;
> + if (brbe_num_branch_records(cpu_pmu))
> + cpu_pmu->pmu.sched_task = armv8pmu_sched_task;
>
> cpu_pmu->name = name;
> cpu_pmu->map_event = map_event;
> diff --git a/include/linux/perf/arm_pmu.h b/include/linux/perf/arm_pmu.h
> index 6dc5e0cd76ca..93c9a26492fc 100644
> --- a/include/linux/perf/arm_pmu.h
> +++ b/include/linux/perf/arm_pmu.h
> @@ -70,6 +70,11 @@ struct pmu_hw_events {
> struct arm_pmu *percpu_pmu;
>
> int irq;
> +
> + struct perf_branch_stack *branch_stack;
> +
> + /* Active events requesting branch records */
> + unsigned int branch_users;
> };
>
> enum armpmu_attr_groups {
> @@ -115,6 +120,7 @@ struct arm_pmu {
> /* PMUv3 only */
> int pmuver;
> u64 reg_pmmir;
> + u64 reg_brbidr;
> #define ARMV8_PMUV3_MAX_COMMON_EVENTS 0x40
> DECLARE_BITMAP(pmceid_bitmap, ARMV8_PMUV3_MAX_COMMON_EVENTS);
> #define ARMV8_PMUV3_EXT_COMMON_EVENT_BASE 0x4000
> @@ -126,6 +132,8 @@ struct arm_pmu {
>
> #define to_arm_pmu(p) (container_of(p, struct arm_pmu, pmu))
>
> +DECLARE_PER_CPU(struct arm_pmu *, cpu_armpmu);
> +
> u64 armpmu_event_update(struct perf_event *event);
>
> int armpmu_event_set_period(struct perf_event *event);
>
tested-by: Adam Young<admiyo@...amperecomputing.com>
Built and run on a BRBE capable machine.
Built userland perf tool. With these, I can build the bubble sort
program posted here:
https://gcc.gnu.org/wiki/AutoFDO/Tutorial
and run
perf record --branch-filter any,save_type,u ./sort
And will generate a perf.data file.
The mechanism applies cleanly and produced what looks like sane output.
Using autofdo to convert to a gcov format created a file that could be
included in a gcc build as profiling data.
~/autofdo/build/create_gcov --binary ./sort --profile ./perf.data
produces fbdata.afdo which can be used to make a profiled build.
gcc -O3 sort.c -o sort_fdo_ified -fprofile-use=fbdata.afdo
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