[PATCH v2 07/10] powerpc/perf: support BHRB disable bit and new filtering modes
Michael Neuling
mikey at neuling.org
Tue Jul 7 17:17:55 AEST 2020
On Wed, 2020-07-01 at 05:20 -0400, Athira Rajeev wrote:
> PowerISA v3.1 has few updates for the Branch History Rolling Buffer(BHRB).
> First is the addition of BHRB disable bit and second new filtering
> modes for BHRB.
>
> BHRB disable is controlled via Monitor Mode Control Register A (MMCRA)
> bit 26, namely "BHRB Recording Disable (BHRBRD)". This field controls
> whether BHRB entries are written when BHRB recording is enabled by other
> bits. Patch implements support for this BHRB disable bit.
Probably good to note here that this is backwards compatible. So if you have a
kernel that doesn't know about this bit, it'll clear it and hence you still get
BHRB.
You should also note why you'd want to do disable this (ie. the core will run
faster).
> Secondly PowerISA v3.1 introduce filtering support for
> PERF_SAMPLE_BRANCH_IND_CALL/COND. The patch adds BHRB filter support
> for "ind_call" and "cond" in power10_bhrb_filter_map().
>
> 'commit bb19af816025 ("powerpc/perf: Prevent kernel address leak to userspace
> via BHRB buffer")'
> added a check in bhrb_read() to filter the kernel address from BHRB buffer.
> Patch here modified
> it to avoid that check for PowerISA v3.1 based processors, since PowerISA v3.1
> allows
> only MSR[PR]=1 address to be written to BHRB buffer.
>
> Signed-off-by: Athira Rajeev <atrajeev at linux.vnet.ibm.com>
> ---
> arch/powerpc/perf/core-book3s.c | 27 +++++++++++++++++++++------
> arch/powerpc/perf/isa207-common.c | 13 +++++++++++++
> arch/powerpc/perf/power10-pmu.c | 13 +++++++++++--
> arch/powerpc/platforms/powernv/idle.c | 14 ++++++++++++++
This touches the idle code so we should get those guys on CC (adding Vaidy and
Ego).
> 4 files changed, 59 insertions(+), 8 deletions(-)
>
> diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
> index fad5159..9709606 100644
> --- a/arch/powerpc/perf/core-book3s.c
> +++ b/arch/powerpc/perf/core-book3s.c
> @@ -466,9 +466,13 @@ static void power_pmu_bhrb_read(struct perf_event *event,
> struct cpu_hw_events *
> * addresses at this point. Check the privileges before
> * exporting it to userspace (avoid exposure of regions
> * where we could have speculative execution)
> + * Incase of ISA 310, BHRB will capture only user-space
> + * address,hence include a check before filtering code
> */
> - if (is_kernel_addr(addr) && perf_allow_kernel(&event-
> >attr) != 0)
> - continue;
> + if (!(ppmu->flags & PPMU_ARCH_310S))
> + if (is_kernel_addr(addr) &&
> + perf_allow_kernel(&event->attr) != 0)
> + continue;
>
> /* Branches are read most recent first (ie. mfbhrb 0 is
> * the most recent branch).
> @@ -1212,7 +1216,7 @@ static void write_mmcr0(struct cpu_hw_events *cpuhw,
> unsigned long mmcr0)
> static void power_pmu_disable(struct pmu *pmu)
> {
> struct cpu_hw_events *cpuhw;
> - unsigned long flags, mmcr0, val;
> + unsigned long flags, mmcr0, val, mmcra = 0;
>
> if (!ppmu)
> return;
> @@ -1245,12 +1249,23 @@ static void power_pmu_disable(struct pmu *pmu)
> mb();
> isync();
>
> + val = mmcra = cpuhw->mmcr[2];
> +
> /*
> * Disable instruction sampling if it was enabled
> */
> - if (cpuhw->mmcr[2] & MMCRA_SAMPLE_ENABLE) {
> - mtspr(SPRN_MMCRA,
> - cpuhw->mmcr[2] & ~MMCRA_SAMPLE_ENABLE);
> + if (cpuhw->mmcr[2] & MMCRA_SAMPLE_ENABLE)
> + mmcra = cpuhw->mmcr[2] & ~MMCRA_SAMPLE_ENABLE;
> +
> + /* Disable BHRB via mmcra [:26] for p10 if needed */
> + if (!(cpuhw->mmcr[2] & MMCRA_BHRB_DISABLE))
> + mmcra |= MMCRA_BHRB_DISABLE;
> +
> + /* Write SPRN_MMCRA if mmcra has either disabled
> + * instruction sampling or BHRB
> + */
> + if (val != mmcra) {
> + mtspr(SPRN_MMCRA, mmcra);
> mb();
> isync();
> }
> diff --git a/arch/powerpc/perf/isa207-common.c b/arch/powerpc/perf/isa207-
> common.c
> index 7d4839e..463d925 100644
> --- a/arch/powerpc/perf/isa207-common.c
> +++ b/arch/powerpc/perf/isa207-common.c
> @@ -404,6 +404,12 @@ int isa207_compute_mmcr(u64 event[], int n_ev,
>
> mmcra = mmcr1 = mmcr2 = mmcr3 = 0;
>
> + /* Disable bhrb unless explicitly requested
> + * by setting MMCRA [:26] bit.
> + */
> + if (cpu_has_feature(CPU_FTR_ARCH_31))
> + mmcra |= MMCRA_BHRB_DISABLE;
> +
> /* Second pass: assign PMCs, set all MMCR1 fields */
> for (i = 0; i < n_ev; ++i) {
> pmc = (event[i] >> EVENT_PMC_SHIFT) & EVENT_PMC_MASK;
> @@ -475,10 +481,17 @@ int isa207_compute_mmcr(u64 event[], int n_ev,
> }
>
> if (event[i] & EVENT_WANTS_BHRB) {
> + /* set MMCRA[:26] to 0 for Power10 to enable BHRB */
> + if (cpu_has_feature(CPU_FTR_ARCH_31))
> + mmcra &= ~MMCRA_BHRB_DISABLE;
> val = (event[i] >> EVENT_IFM_SHIFT) & EVENT_IFM_MASK;
> mmcra |= val << MMCRA_IFM_SHIFT;
> }
>
> + /* set MMCRA[:26] to 0 if there is user request for BHRB */
> + if (cpu_has_feature(CPU_FTR_ARCH_31) &&
> has_branch_stack(pevents[i]))
> + mmcra &= ~MMCRA_BHRB_DISABLE;
> +
> if (pevents[i]->attr.exclude_user)
> mmcr2 |= MMCR2_FCP(pmc);
>
> diff --git a/arch/powerpc/perf/power10-pmu.c b/arch/powerpc/perf/power10-pmu.c
> index d64d69d..07fb919 100644
> --- a/arch/powerpc/perf/power10-pmu.c
> +++ b/arch/powerpc/perf/power10-pmu.c
> @@ -82,6 +82,8 @@
>
> /* MMCRA IFM bits - POWER10 */
> #define POWER10_MMCRA_IFM1 0x0000000040000000UL
> +#define POWER10_MMCRA_IFM2 0x0000000080000000UL
> +#define POWER10_MMCRA_IFM3 0x00000000C0000000UL
> #define POWER10_MMCRA_BHRB_MASK 0x00000000C0000000UL
>
> /* Table of alternatives, sorted by column 0 */
> @@ -233,8 +235,15 @@ static u64 power10_bhrb_filter_map(u64
> branch_sample_type)
> if (branch_sample_type & PERF_SAMPLE_BRANCH_ANY_RETURN)
> return -1;
>
> - if (branch_sample_type & PERF_SAMPLE_BRANCH_IND_CALL)
> - return -1;
> + if (branch_sample_type & PERF_SAMPLE_BRANCH_IND_CALL) {
> + pmu_bhrb_filter |= POWER10_MMCRA_IFM2;
> + return pmu_bhrb_filter;
> + }
> +
> + if (branch_sample_type & PERF_SAMPLE_BRANCH_COND) {
> + pmu_bhrb_filter |= POWER10_MMCRA_IFM3;
> + return pmu_bhrb_filter;
> + }
>
> if (branch_sample_type & PERF_SAMPLE_BRANCH_CALL)
> return -1;
> diff --git a/arch/powerpc/platforms/powernv/idle.c
> b/arch/powerpc/platforms/powernv/idle.c
> index 2dd4673..7db99c7 100644
> --- a/arch/powerpc/platforms/powernv/idle.c
> +++ b/arch/powerpc/platforms/powernv/idle.c
> @@ -611,6 +611,7 @@ static unsigned long power9_idle_stop(unsigned long psscr,
> bool mmu_on)
> unsigned long srr1;
> unsigned long pls;
> unsigned long mmcr0 = 0;
> + unsigned long mmcra_bhrb = 0;
> struct p9_sprs sprs = {}; /* avoid false used-uninitialised */
> bool sprs_saved = false;
>
> @@ -657,6 +658,15 @@ static unsigned long power9_idle_stop(unsigned long
> psscr, bool mmu_on)
> */
> mmcr0 = mfspr(SPRN_MMCR0);
> }
> +
> + if (cpu_has_feature(CPU_FTR_ARCH_31)) {
> + /* POWER10 uses MMCRA[:26] as BHRB disable bit
> + * to disable BHRB logic when not used. Hence Save and
> + * restore MMCRA after a state-loss idle.
> + */
> + mmcra_bhrb = mfspr(SPRN_MMCRA);
Why is the bhrb bit of mmcra special here?
> + }
> +
> if ((psscr & PSSCR_RL_MASK) >= pnv_first_spr_loss_level) {
> sprs.lpcr = mfspr(SPRN_LPCR);
> sprs.hfscr = mfspr(SPRN_HFSCR);
> @@ -721,6 +731,10 @@ static unsigned long power9_idle_stop(unsigned long
> psscr, bool mmu_on)
> mtspr(SPRN_MMCR0, mmcr0);
> }
>
> + /* Reload MMCRA to restore BHRB disable bit for POWER10 */
> + if (cpu_has_feature(CPU_FTR_ARCH_31))
> + mtspr(SPRN_MMCRA, mmcra_bhrb);
> +
> /*
> * DD2.2 and earlier need to set then clear bit 60 in MMCRA
> * to ensure the PMU starts running.
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