From: Mark Rutland <mark.rutland@arm.com>
To: Julien Thierry <julien.thierry@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 16:06:39 +0100 [thread overview]
Message-ID: <20190708150639.GE33099@lakrids.cambridge.arm.com> (raw)
In-Reply-To: <1562596377-33196-4-git-send-email-julien.thierry@arm.com>
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?
>
> 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?
Otherwise, this looks good to me.
Thanks,
Mark.
> +
> /*
> * Get and reset the IRQ flags
> */
> @@ -1004,6 +1019,8 @@ static irqreturn_t armv7pmu_handle_irq(struct arm_pmu *cpu_pmu)
> */
> irq_work_run();
>
> + armv7_pmsel_write(pmsel);
> +
> return IRQ_HANDLED;
> }
>
> --
> 1.9.1
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next prev parent reply other threads:[~2019-07-08 15:06 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 [this message]
2019-07-08 15:40 ` Julien Thierry
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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