Message-ID: <83ec74cb-02c3-4be4-a182-c2c69619abaf@nvidia.com>
Date: Wed, 24 Sep 2025 23:33:31 -0700
From: Fenghua Yu <fenghuay@...dia.com>
To: James Morse <james.morse@....com>, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-acpi@...r.kernel.org
Cc: D Scott Phillips OS <scott@...amperecomputing.com>,
 carl@...amperecomputing.com, lcherian@...vell.com,
 bobo.shaobowang@...wei.com, tan.shaopeng@...itsu.com,
 baolin.wang@...ux.alibaba.com, Xin Hao <xhao@...ux.alibaba.com>,
 peternewman@...gle.com, dfustini@...libre.com, amitsinght@...vell.com,
 David Hildenbrand <david@...hat.com>, Dave Martin <dave.martin@....com>,
 Koba Ko <kobak@...dia.com>, Shanker Donthineni <sdonthineni@...dia.com>,
 baisheng.gao@...soc.com, Jonathan Cameron <jonathan.cameron@...wei.com>,
 Rob Herring <robh@...nel.org>, Rohit Mathew <rohit.mathew@....com>,
 Rafael Wysocki <rafael@...nel.org>, Len Brown <lenb@...nel.org>,
 Lorenzo Pieralisi <lpieralisi@...nel.org>, Hanjun Guo
 <guohanjun@...wei.com>, Sudeep Holla <sudeep.holla@....com>,
 Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Danilo Krummrich <dakr@...nel.org>
Subject: Re: [PATCH v2 18/29] arm_mpam: Register and enable IRQs

Hi, James,

On 9/10/25 13:42, James Morse wrote:
> Register and enable error IRQs. All the MPAM error interrupts indicate a
> software bug, e.g. out of range partid. If the error interrupt is ever
> signalled, attempt to disable MPAM.
>
> Only the irq handler accesses the ESR register, so no locking is needed.
> The work to disable MPAM after an error needs to happen at process
> context as it takes mutex. It also unregisters the interrupts, meaning
> it can't be done from the threaded part of a threaded interrupt.
> Instead, mpam_disable() gets scheduled.
>
> Enabling the IRQs in the MSC may involve cross calling to a CPU that
> can access the MSC.
>
> Once the IRQ is requested, the mpam_disable() path can be called
> asynchronously, which will walk structures sized by max_partid. Ensure
> this size is fixed before the interrupt is requested.
>
> CC: Rohit Mathew <rohit.mathew@....com>
> Tested-by: Rohit Mathew <rohit.mathew@....com>
> Signed-off-by: James Morse <james.morse@....com>
> ---
> Changes since v1:
>   * Made mpam_unregister_irqs() safe to race with itself.
>   * Removed threaded interrupts.
>   * Schedule mpam_disable() from cpuhp callback in the case of an error.
>   * Added mpam_disable_reason.
>   * Use alloc_percpu()
>
> Changes since RFC:
>   * Use guard marco when walking srcu list.
>   * Use INTEN macro for enabling interrupts.
>   * Move partid_max_published up earlier in mpam_enable_once().
> ---
>   drivers/resctrl/mpam_devices.c  | 277 +++++++++++++++++++++++++++++++-
>   drivers/resctrl/mpam_internal.h |  10 ++
>   2 files changed, 284 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
> index a9d3c4b09976..e7e4afc1ea95 100644
> --- a/drivers/resctrl/mpam_devices.c
> +++ b/drivers/resctrl/mpam_devices.c
> @@ -14,6 +14,9 @@
>   #include <linux/device.h>
>   #include <linux/errno.h>
>   #include <linux/gfp.h>
> +#include <linux/interrupt.h>
> +#include <linux/irq.h>
> +#include <linux/irqdesc.h>
>   #include <linux/list.h>
>   #include <linux/lockdep.h>
>   #include <linux/mutex.h>
> @@ -166,6 +169,24 @@ static u64 mpam_msc_read_idr(struct mpam_msc *msc)
>   	return (idr_high << 32) | idr_low;
>   }
>   
> +static void mpam_msc_zero_esr(struct mpam_msc *msc)
> +{
> +	__mpam_write_reg(msc, MPAMF_ESR, 0);
> +	if (msc->has_extd_esr)
> +		__mpam_write_reg(msc, MPAMF_ESR + 4, 0);
> +}
> +
> +static u64 mpam_msc_read_esr(struct mpam_msc *msc)
> +{
> +	u64 esr_high = 0, esr_low;
> +
> +	esr_low = __mpam_read_reg(msc, MPAMF_ESR);
> +	if (msc->has_extd_esr)
> +		esr_high = __mpam_read_reg(msc, MPAMF_ESR + 4);
> +
> +	return (esr_high << 32) | esr_low;
> +}
> +
>   static void __mpam_part_sel_raw(u32 partsel, struct mpam_msc *msc)
>   {
>   	lockdep_assert_held(&msc->part_sel_lock);
> @@ -754,6 +775,7 @@ static int mpam_msc_hw_probe(struct mpam_msc *msc)
>   		pmg_max = FIELD_GET(MPAMF_IDR_PMG_MAX, idr);
>   		msc->partid_max = min(msc->partid_max, partid_max);
>   		msc->pmg_max = min(msc->pmg_max, pmg_max);
> +		msc->has_extd_esr = FIELD_GET(MPAMF_IDR_HAS_EXTD_ESR, idr);
>   
>   		mutex_lock(&mpam_list_lock);
>   		ris = mpam_get_or_create_ris(msc, ris_idx);
> @@ -768,6 +790,9 @@ static int mpam_msc_hw_probe(struct mpam_msc *msc)
>   		mutex_unlock(&msc->part_sel_lock);
>   	}
>   
> +	/* Clear any stale errors */
> +	mpam_msc_zero_esr(msc);
> +
>   	spin_lock(&partid_max_lock);
>   	mpam_partid_max = min(mpam_partid_max, msc->partid_max);
>   	mpam_pmg_max = min(mpam_pmg_max, msc->pmg_max);
> @@ -895,6 +920,13 @@ static void mpam_reset_msc(struct mpam_msc *msc, bool online)
>   	}
>   }
>   
> +static void _enable_percpu_irq(void *_irq)
> +{
> +	int *irq = _irq;
> +
> +	enable_percpu_irq(*irq, IRQ_TYPE_NONE);
> +}
> +
>   static int mpam_cpu_online(unsigned int cpu)
>   {
>   	int idx;
> @@ -906,6 +938,9 @@ static int mpam_cpu_online(unsigned int cpu)
>   		if (!cpumask_test_cpu(cpu, &msc->accessibility))
>   			continue;
>   
> +		if (msc->reenable_error_ppi)
> +			_enable_percpu_irq(&msc->reenable_error_ppi);
> +
>   		if (atomic_fetch_inc(&msc->online_refs) == 0)
>   			mpam_reset_msc(msc, true);
>   	}
> @@ -959,6 +994,9 @@ static int mpam_cpu_offline(unsigned int cpu)
>   		if (!cpumask_test_cpu(cpu, &msc->accessibility))
>   			continue;
>   
> +		if (msc->reenable_error_ppi)
> +			disable_percpu_irq(msc->reenable_error_ppi);
> +
>   		if (atomic_dec_and_test(&msc->online_refs))
>   			mpam_reset_msc(msc, false);
>   	}
> @@ -985,6 +1023,51 @@ static void mpam_register_cpuhp_callbacks(int (*online)(unsigned int online),
>   	mutex_unlock(&mpam_cpuhp_state_lock);
>   }
>   
> +static int __setup_ppi(struct mpam_msc *msc)
> +{
> +	int cpu;
> +	struct device *dev = &msc->pdev->dev;
> +
> +	msc->error_dev_id = alloc_percpu(struct mpam_msc *);
> +	if (!msc->error_dev_id)
> +		return -ENOMEM;
> +
> +	for_each_cpu(cpu, &msc->accessibility) {
> +		struct mpam_msc *empty = *per_cpu_ptr(msc->error_dev_id, cpu);
> +
> +		if (empty) {
> +			dev_err_once(dev, "MSC shares PPI with %s!\n",
> +				     dev_name(&empty->pdev->dev));
> +			return -EBUSY;
> +		}
> +		*per_cpu_ptr(msc->error_dev_id, cpu) = msc;
> +	}
> +
> +	return 0;
> +}
> +
> +static int mpam_msc_setup_error_irq(struct mpam_msc *msc)
> +{
> +	int irq;
> +
> +	irq = platform_get_irq_byname_optional(msc->pdev, "error");
> +	if (irq <= 0)
> +		return 0;
> +
> +	/* Allocate and initialise the percpu device pointer for PPI */
> +	if (irq_is_percpu(irq))
> +		return __setup_ppi(msc);
> +
> +	/* sanity check: shared interrupts can be routed anywhere? */
> +	if (!cpumask_equal(&msc->accessibility, cpu_possible_mask)) {
> +		pr_err_once("msc:%u is a private resource with a shared error interrupt",
> +			    msc->id);
> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +
>   /*
>    * An MSC can control traffic from a set of CPUs, but may only be accessible
>    * from a (hopefully wider) set of CPUs. The common reason for this is power
> @@ -1060,6 +1143,10 @@ static int mpam_msc_drv_probe(struct platform_device *pdev)
>   			break;
>   		}
>   
> +		err = mpam_msc_setup_error_irq(msc);
> +		if (err)
> +			break;
> +
>   		if (device_property_read_u32(&pdev->dev, "pcc-channel",
>   					     &msc->pcc_subspace_id))
>   			msc->iface = MPAM_IFACE_MMIO;
> @@ -1318,11 +1405,172 @@ static void mpam_enable_merge_features(struct list_head *all_classes_list)
>   	}
>   }
>   
> +static char *mpam_errcode_names[16] = {
> +	[0] = "No error",
> +	[1] = "PARTID_SEL_Range",
> +	[2] = "Req_PARTID_Range",
> +	[3] = "MSMONCFG_ID_RANGE",
> +	[4] = "Req_PMG_Range",
> +	[5] = "Monitor_Range",
> +	[6] = "intPARTID_Range",
> +	[7] = "Unexpected_INTERNAL",
> +	[8] = "Undefined_RIS_PART_SEL",
> +	[9] = "RIS_No_Control",
> +	[10] = "Undefined_RIS_MON_SEL",
> +	[11] = "RIS_No_Monitor",
> +	[12 ... 15] = "Reserved"
> +};
> +
> +static int mpam_enable_msc_ecr(void *_msc)
> +{
> +	struct mpam_msc *msc = _msc;
> +
> +	__mpam_write_reg(msc, MPAMF_ECR, MPAMF_ECR_INTEN);
> +
> +	return 0;
> +}
> +
> +/* This can run in mpam_disable(), and the interrupt handler on the same CPU */
> +static int mpam_disable_msc_ecr(void *_msc)
> +{
> +	struct mpam_msc *msc = _msc;
> +
> +	__mpam_write_reg(msc, MPAMF_ECR, 0);
> +
> +	return 0;
> +}
> +
> +static irqreturn_t __mpam_irq_handler(int irq, struct mpam_msc *msc)
> +{
> +	u64 reg;
> +	u16 partid;
> +	u8 errcode, pmg, ris;
> +
> +	if (WARN_ON_ONCE(!msc) ||
> +	    WARN_ON_ONCE(!cpumask_test_cpu(smp_processor_id(),
> +					   &msc->accessibility)))
> +		return IRQ_NONE;
> +
> +	reg = mpam_msc_read_esr(msc);
> +
> +	errcode = FIELD_GET(MPAMF_ESR_ERRCODE, reg);
> +	if (!errcode)
> +		return IRQ_NONE;
> +
> +	/* Clear level triggered irq */
> +	mpam_msc_zero_esr(msc);
> +
> +	partid = FIELD_GET(MPAMF_ESR_PARTID_MON, reg);
> +	pmg = FIELD_GET(MPAMF_ESR_PMG, reg);
> +	ris = FIELD_GET(MPAMF_ESR_RIS, reg);
> +
> +	pr_err_ratelimited("error irq from msc:%u '%s', partid:%u, pmg: %u, ris: %u\n",
> +			   msc->id, mpam_errcode_names[errcode], partid, pmg,
> +			   ris);
> +
> +	/* Disable this interrupt. */
> +	mpam_disable_msc_ecr(msc);
> +
> +	/*
> +	 * Schedule the teardown work. Don't use a threaded IRQ as we can't
> +	 * unregister the interrupt from the threaded part of the handler.
> +	 */
> +	mpam_disable_reason = "hardware error interrupt";
> +	schedule_work(&mpam_broken_work);
> +
> +	return IRQ_HANDLED;
> +}
> +
> +static irqreturn_t mpam_ppi_handler(int irq, void *dev_id)
> +{
> +	struct mpam_msc *msc = *(struct mpam_msc **)dev_id;
> +
> +	return __mpam_irq_handler(irq, msc);
> +}
> +
> +static irqreturn_t mpam_spi_handler(int irq, void *dev_id)
> +{
> +	struct mpam_msc *msc = dev_id;
> +
> +	return __mpam_irq_handler(irq, msc);
> +}
> +
> +static int mpam_register_irqs(void)
> +{
> +	int err, irq;
> +	struct mpam_msc *msc;
> +
> +	lockdep_assert_cpus_held();
> +
> +	guard(srcu)(&mpam_srcu);
> +	list_for_each_entry_srcu(msc, &mpam_all_msc, all_msc_list,
> +				 srcu_read_lock_held(&mpam_srcu)) {
> +		irq = platform_get_irq_byname_optional(msc->pdev, "error");
> +		if (irq <= 0)
> +			continue;
> +
> +		/* The MPAM spec says the interrupt can be SPI, PPI or LPI */
> +		/* We anticipate sharing the interrupt with other MSCs */
> +		if (irq_is_percpu(irq)) {
> +			err = request_percpu_irq(irq, &mpam_ppi_handler,
> +						 "mpam:msc:error",
> +						 msc->error_dev_id);
> +			if (err)
> +				return err;
> +
> +			msc->reenable_error_ppi = irq;
> +			smp_call_function_many(&msc->accessibility,
> +					       &_enable_percpu_irq, &irq,
> +					       true);
> +		} else {
> +			err = devm_request_irq(&msc->pdev->dev,irq,
> +					       &mpam_spi_handler, IRQF_SHARED,
> +					       "mpam:msc:error", msc);
> +			if (err)
> +				return err;
> +		}
> +
> +		set_bit(MPAM_ERROR_IRQ_REQUESTED, &msc->error_irq_flags);
> +		mpam_touch_msc(msc, mpam_enable_msc_ecr, msc);
> +		set_bit(MPAM_ERROR_IRQ_HW_ENABLED, &msc->error_irq_flags);
> +	}
> +
> +	return 0;
> +}
> +
> +static void mpam_unregister_irqs(void)
> +{
> +	int irq, idx;
> +	struct mpam_msc *msc;
> +
> +	cpus_read_lock();
> +	/* take the lock as free_irq() can sleep */
> +	idx = srcu_read_lock(&mpam_srcu);
guard(srcu)(&mpam_srcu);
> +	list_for_each_entry_srcu(msc, &mpam_all_msc, all_msc_list,
> +				 srcu_read_lock_held(&mpam_srcu)) {
> +		irq = platform_get_irq_byname_optional(msc->pdev, "error");
> +		if (irq <= 0)
> +			continue;
> +
> +		if (test_and_clear_bit(MPAM_ERROR_IRQ_HW_ENABLED, &msc->error_irq_flags))
> +			mpam_touch_msc(msc, mpam_disable_msc_ecr, msc);
> +
> +		if (test_and_clear_bit(MPAM_ERROR_IRQ_REQUESTED, &msc->error_irq_flags)) {
> +			if (irq_is_percpu(irq)) {
> +				msc->reenable_error_ppi = 0;
> +				free_percpu_irq(irq, msc->error_dev_id);
> +			} else {
> +				devm_free_irq(&msc->pdev->dev, irq, msc);
> +			}
> +		}
> +	}
> +	srcu_read_unlock(&mpam_srcu, idx);
> +	cpus_read_unlock();
> +}
> +

[SNIP]

Thanks.

-Fenghua

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