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Message-ID: <20251003132236.00002ecd@huawei.com>
Date: Fri, 3 Oct 2025 13:22:36 +0100
From: Jonathan Cameron <jonathan.cameron@...wei.com>
To: Bharata B Rao <bharata@....com>
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Subject: Re: [RFC PATCH v2 5/8] x86: ibs: Enable IBS profiling for memory
accesses
On Wed, 10 Sep 2025 20:16:50 +0530
Bharata B Rao <bharata@....com> wrote:
> Enable IBS memory access data collection for user memory
> accesses by programming the required MSRs. The profiling
> is turned ON only for user mode execution and turned OFF
> for kernel mode execution. Profiling is explicitly disabled
> for NMI handler too.
>
> TODOs:
>
> - IBS sampling rate is kept fixed for now.
> - Arch/vendor separation/isolation of the code needs relook.
>
> Signed-off-by: Bharata B Rao <bharata@....com>
One "oops I misread it" wrt to review of previous patch.
+ a really trivial thing.
J
> ---
> arch/x86/include/asm/entry-common.h | 3 +++
> arch/x86/include/asm/hardirq.h | 2 ++
> arch/x86/include/asm/ibs.h | 2 ++
> arch/x86/mm/ibs.c | 32 +++++++++++++++++++++++++++++
> 4 files changed, 39 insertions(+)
> diff --git a/arch/x86/mm/ibs.c b/arch/x86/mm/ibs.c
> index 6669710dd35b..3128e8fa5f39 100644
> --- a/arch/x86/mm/ibs.c
> +++ b/arch/x86/mm/ibs.c
> @@ -16,6 +16,7 @@ static u64 ibs_config __read_mostly;
> static u32 ibs_caps;
>
> #define IBS_NR_SAMPLES 150
> +#define IBS_SAMPLE_PERIOD 10000
>
> /*
> * Basic access info captured for each memory access.
> @@ -98,6 +99,36 @@ static void ibs_irq_handler(struct irq_work *i)
> schedule_work_on(smp_processor_id(), &ibs_work);
> }
>
> +void hw_access_profiling_stop(void)
> +{
> + u64 ops_ctl;
> +
> + if (!arch_hw_access_profiling)
> + return;
> +
> + rdmsrl(MSR_AMD64_IBSOPCTL, ops_ctl);
> + wrmsrl(MSR_AMD64_IBSOPCTL, ops_ctl & ~IBS_OP_ENABLE);
> +}
> +
> +void hw_access_profiling_start(void)
> +{
> + u64 config = 0;
> + unsigned int period = IBS_SAMPLE_PERIOD;
> +
> + if (!arch_hw_access_profiling)
> + return;
> +
> + /* Disable IBS for kernel thread */
> + if (!current->mm)
> + goto out;
> +
> + config = (period >> 4) & IBS_OP_MAX_CNT;
Bonus space though before & that can go.
> + config |= (period & IBS_OP_MAX_CNT_EXT_MASK);
> + config |= ibs_config;
Ah. Ignore comment in previous patch on this not being global. Clearly it needs
to be. Oops I misread this earlier.
> +out:
> + wrmsrl(MSR_AMD64_IBSOPCTL, config);
> +}
> +
> /*
> * IBS NMI handler: Process the memory access info reported by IBS.
> *
> @@ -304,6 +335,7 @@ static int __init ibs_access_profiling_init(void)
> x86_amd_ibs_access_profile_startup,
> x86_amd_ibs_access_profile_teardown);
>
> + arch_hw_access_profiling = true;
> pr_info("IBS setup for memory access profiling\n");
> return 0;
> }
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