From: Julien Thierry <julien.thierry@arm.com>
To: Mark Rutland <mark.rutland@arm.com>
Cc: peterz@infradead.org, liwei391@huawei.com, will.deacon@arm.com,
Russell King <linux@armlinux.org.uk>,
acme@kernel.org, alexander.shishkin@linux.intel.com,
mingo@redhat.com, namhyung@kernel.org, jolsa@redhat.com,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v3 3/9] arm: perf: save/resore pmsel
Date: Mon, 8 Jul 2019 16:40:48 +0100 [thread overview]
Message-ID: <b2e95aab-bd01-faad-a548-ef6677cab991@arm.com> (raw)
In-Reply-To: <20190708150639.GE33099@lakrids.cambridge.arm.com>
On 08/07/2019 16:06, Mark Rutland wrote:
> On Mon, Jul 08, 2019 at 03:32:51PM +0100, Julien Thierry wrote:
>> The callback pmu->read() can be called with interrupts enabled.
>> Currently, on ARM, this can cause the following callchain:
>>
>> armpmu_read() -> armpmu_event_update() -> armv7pmu_read_counter()
>>
>> The last function might modify the counter selector register and then
>> read the target counter, without taking any lock. With interrupts
>> enabled, a PMU interrupt could occur and modify the selector register
>> as well, between the selection and read of the interrupted context.
>>
>> Save and restore the value of the selector register in the PMU interrupt
>> handler, ensuring the interrupted context is left with the correct PMU
>> registers selected.
>
> IIUC, this is a latent bug, so I guess it should be Cc'd stable?
>
It's my understanding as well. I'll put stable in copy for next iteration.
>>
>> Signed-off-by: Julien Thierry <julien.thierry@arm.com>
>> Cc: Will Deacon <will.deacon@arm.com>
>> 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: Alexander Shishkin <alexander.shishkin@linux.intel.com>
>> Cc: Jiri Olsa <jolsa@redhat.com>
>> Cc: Namhyung Kim <namhyung@kernel.org>
>> Cc: Russell King <linux@armlinux.org.uk>
>> ---
>> arch/arm/kernel/perf_event_v7.c | 21 +++++++++++++++++++--
>> 1 file changed, 19 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/arm/kernel/perf_event_v7.c b/arch/arm/kernel/perf_event_v7.c
>> index a4fb0f8..c3da7a5 100644
>> --- a/arch/arm/kernel/perf_event_v7.c
>> +++ b/arch/arm/kernel/perf_event_v7.c
>> @@ -736,10 +736,22 @@ static inline int armv7_pmnc_counter_has_overflowed(u32 pmnc, int idx)
>> return pmnc & BIT(ARMV7_IDX_TO_COUNTER(idx));
>> }
>>
>> -static inline void armv7_pmnc_select_counter(int idx)
>> +static inline u32 armv7_pmsel_read(void)
>> +{
>> + u32 pmsel;
>> +
>> + asm volatile("mrc p15, 0, %0, c9, c12, 5" : "=&r" (pmsel));
>> + return pmsel;
>> +}
>> +
>> +static inline void armv7_pmsel_write(u32 counter)
>> {
>> - u32 counter = ARMV7_IDX_TO_COUNTER(idx);
>> asm volatile("mcr p15, 0, %0, c9, c12, 5" : : "r" (counter));
>> +}
>> +
>> +static inline void armv7_pmnc_select_counter(int idx)
>> +{
>> + armv7_pmsel_write(ARMV7_IDX_TO_COUNTER(idx));
>> isb();
>> }
>>
>> @@ -952,8 +964,11 @@ static irqreturn_t armv7pmu_handle_irq(struct arm_pmu *cpu_pmu)
>> struct perf_sample_data data;
>> struct pmu_hw_events *cpuc = this_cpu_ptr(cpu_pmu->hw_events);
>> struct pt_regs *regs;
>> + u32 pmsel;
>> int idx;
>>
>> + pmsel = armv7_pmsel_read();
>
> Could we add a comment explaining why we need to save/restore this?
>
Sure, will do.
> Otherwise, this looks good to me.
Thanks,
--
Julien Thierry
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next prev parent reply other threads:[~2019-07-08 15:40 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-08 14:32 [PATCH v3 0/9] arm_pmu: Use NMI for perf interrupt Julien Thierry
2019-07-08 14:32 ` [PATCH v3 1/9] arm64: perf: avoid PMXEV* indirection Julien Thierry
2019-07-08 15:03 ` Mark Rutland
2019-07-10 10:57 ` Steven Price
2019-07-10 11:01 ` Julien Thierry
2019-07-16 10:33 ` Shijith Thotton
2019-07-16 10:54 ` Julien Thierry
2019-07-17 4:45 ` Shijith Thotton
2019-07-08 14:32 ` [PATCH v3 2/9] arm64: perf: Remove PMU locking Julien Thierry
2019-07-08 15:03 ` Mark Rutland
2019-07-08 15:34 ` Julien Thierry
2019-07-09 11:22 ` Mark Rutland
2019-07-08 14:32 ` [PATCH v3 3/9] arm: perf: save/resore pmsel Julien Thierry
2019-07-08 15:06 ` Mark Rutland
2019-07-08 15:40 ` Julien Thierry [this message]
2019-07-08 14:32 ` [PATCH v3 4/9] arm: perf: Remove Remove PMU locking Julien Thierry
2019-07-08 15:10 ` Mark Rutland
2019-07-08 14:32 ` [PATCH v3 5/9] perf/arm_pmu: Move PMU lock to ARMv6 events Julien Thierry
2019-07-08 15:19 ` Mark Rutland
2019-07-08 15:50 ` Julien Thierry
2019-07-08 14:32 ` [PATCH v3 6/9] arm64: perf: Do not call irq_work_run in NMI context Julien Thierry
2019-07-08 15:29 ` Mark Rutland
2019-07-08 16:00 ` Julien Thierry
2019-07-08 14:32 ` [PATCH v3 7/9] arm/arm64: kvm: pmu: Make overflow handler NMI safe Julien Thierry
2019-07-08 15:30 ` Mark Rutland
2019-07-11 12:38 ` Zenghui Yu
2019-07-08 14:32 ` [PATCH v3 8/9] arm_pmu: Introduce pmu_irq_ops Julien Thierry
2019-07-08 14:32 ` [PATCH v3 9/9] arm_pmu: Use NMIs for PMU Julien Thierry
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