[PATCH] x86/events/amd/iommu: Fix cpumask of IOMMU events

[PATCH] x86/events/amd/iommu: Fix cpumask of IOMMU events

[Vasant Hegde]

IOMMU performance counters are accessed via MMIO space. Currently IOMMU
PMUs uses a single global cpumask (iommu_cpumask) shared across all AMD
IOMMU PMU instances. This prevents collecting per-socket numbers
(ex: perf stat --per-socket).

Fix this by adjusting cpumask based on IOMMUs NUMA node.

Signed-off-by: Vasant Hegde <vasant.hegde@amd.com>
---
 arch/x86/events/amd/iommu.c | 29 +++++++++++++++++++++++------
 drivers/iommu/amd/init.c    |  7 +++++++
 include/linux/amd-iommu.h   |  1 +
 3 files changed, 31 insertions(+), 6 deletions(-)

diff --git a/arch/x86/events/amd/iommu.c b/arch/x86/events/amd/iommu.c
index 07b110e8418a..b1848300028d 100644
--- a/arch/x86/events/amd/iommu.c
+++ b/arch/x86/events/amd/iommu.c
@@ -10,6 +10,7 @@
 
 #define pr_fmt(fmt)	"perf/amd_iommu: " fmt
 
+#include <linux/device.h>
 #include <linux/perf_event.h>
 #include <linux/init.h>
 #include <linux/cpumask.h>
@@ -43,6 +44,7 @@ struct perf_amd_iommu {
 	u8 max_counters;
 	u64 cntr_assign_mask;
 	raw_spinlock_t lock;
+	cpumask_t cpumask;
 };
 
 static LIST_HEAD(perf_amd_iommu_list);
@@ -131,13 +133,15 @@ static struct amd_iommu_event_desc amd_iommu_v2_event_descs[] = {
 /*---------------------------------------------
  * sysfs cpumask attributes
  *---------------------------------------------*/
-static cpumask_t iommu_cpumask;
-
 static ssize_t _iommu_cpumask_show(struct device *dev,
 				   struct device_attribute *attr,
 				   char *buf)
 {
-	return cpumap_print_to_pagebuf(true, buf, &iommu_cpumask);
+	struct pmu *pmu = dev_get_drvdata(dev);
+	struct perf_amd_iommu *perf_iommu =
+			container_of(pmu, struct perf_amd_iommu, pmu);
+
+	return cpumap_print_to_pagebuf(true, buf, &perf_iommu->cpumask);
 }
 static DEVICE_ATTR(cpumask, S_IRUGO, _iommu_cpumask_show, NULL);
 
@@ -420,7 +424,8 @@ static const struct pmu iommu_pmu __initconst = {
 static __init int init_one_iommu(unsigned int idx)
 {
 	struct perf_amd_iommu *perf_iommu;
-	int ret;
+	struct device *dev;
+	int node, cpu, ret;
 
 	perf_iommu = kzalloc_obj(struct perf_amd_iommu);
 	if (!perf_iommu)
@@ -440,6 +445,20 @@ static __init int init_one_iommu(unsigned int idx)
 		return -EINVAL;
 	}
 
+	dev = amd_iommu_idx_to_dev(idx);
+	node = dev ? dev_to_node(dev) : NUMA_NO_NODE;
+	if (node != NUMA_NO_NODE)
+		cpu = cpumask_any_and(cpumask_of_node(node), cpu_online_mask);
+	else
+		cpu = cpumask_any(cpu_online_mask);
+
+	if (cpu >= nr_cpu_ids) {
+		pr_warn("Failed to find online CPU for IOMMU %d.\n", idx);
+		kfree(perf_iommu);
+		return -ENODEV;
+	}
+	cpumask_set_cpu(cpu, &perf_iommu->cpumask);
+
 	snprintf(perf_iommu->name, IOMMU_NAME_SIZE, "amd_iommu_%u", idx);
 
 	ret = perf_pmu_register(&perf_iommu->pmu, perf_iommu->name, -1);
@@ -483,8 +502,6 @@ static __init int amd_iommu_pc_init(void)
 		return -ENODEV;
 	}
 
-	/* Init cpumask attributes to only core 0 */
-	cpumask_set_cpu(0, &iommu_cpumask);
 	return 0;
 }
 
diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
index 3bdb380d23e9..2c35d171b5ae 100644
--- a/drivers/iommu/amd/init.c
+++ b/drivers/iommu/amd/init.c
@@ -3939,6 +3939,13 @@ struct amd_iommu *get_amd_iommu(unsigned int idx)
 	return NULL;
 }
 
+struct device *amd_iommu_idx_to_dev(unsigned int idx)
+{
+	struct amd_iommu *iommu = get_amd_iommu(idx);
+
+	return iommu ? &iommu->dev->dev : NULL;
+}
+
 /****************************************************************************
  *
  * IOMMU EFR Performance Counter support functionality. This code allows
diff --git a/include/linux/amd-iommu.h b/include/linux/amd-iommu.h
index edcee9f5335a..6b8d6b53b4e9 100644
--- a/include/linux/amd-iommu.h
+++ b/include/linux/amd-iommu.h
@@ -67,6 +67,7 @@ int amd_iommu_pc_set_reg(struct amd_iommu *iommu, u8 bank, u8 cntr, u8 fxn,
 int amd_iommu_pc_get_reg(struct amd_iommu *iommu, u8 bank, u8 cntr, u8 fxn,
 		u64 *value);
 struct amd_iommu *get_amd_iommu(unsigned int idx);
+struct device *amd_iommu_idx_to_dev(unsigned int idx);
 
 #ifdef CONFIG_KVM_AMD_SEV
 int amd_iommu_snp_disable(void);
-- 
2.31.1

Re: [PATCH] x86/events/amd/iommu: Fix cpumask of IOMMU events

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] PMU initialization fails for IOMMUs located on NUMA nodes without online CPUs.
--

commit ef1363d0a37870d7cf1f1095cd3ebf42cc5a8bdc
Author: Vasant Hegde <vasant.hegde@amd.com>

x86/events/amd/iommu: Fix cpumask of IOMMU events

This commit changes the IOMMU PMU cpumask from a single global mask to a
per-IOMMU mask based on the NUMA node of the IOMMU, allowing per-socket
performance counter collection.

> diff --git a/arch/x86/events/amd/iommu.c b/arch/x86/events/amd/iommu.c
> --- a/arch/x86/events/amd/iommu.c
> +++ b/arch/x86/events/amd/iommu.c
[ ... ]
> @@ -440,6 +445,20 @@ static __init int init_one_iommu(unsigned int idx)
>  		return -EINVAL;
>  	}
>  
> +	dev = amd_iommu_idx_to_dev(idx);
> +	node = dev ? dev_to_node(dev) : NUMA_NO_NODE;
> +	if (node != NUMA_NO_NODE)
> +		cpu = cpumask_any_and(cpumask_of_node(node), cpu_online_mask);

If the IOMMU resides on a CPU-less NUMA node (like a PCIe expansion switch
or a memory-only CXL node), or if all CPUs on that node are currently
offline, will cpumask_any_and() return a value greater than or equal to
nr_cpu_ids?

> +	else
> +		cpu = cpumask_any(cpu_online_mask);
> +
> +	if (cpu >= nr_cpu_ids) {
> +		pr_warn("Failed to find online CPU for IOMMU %d.\n", idx);
> +		kfree(perf_iommu);
> +		return -ENODEV;
> +	}

Could this cause PMU initialization to fail for IOMMUs on CPU-less nodes?

Since AMD IOMMU performance counters are accessed via MMIO space, they can
be driven by any CPU in the system. Would it be better to fall back to
cpumask_any(cpu_online_mask) instead of returning -ENODEV when a local CPU
is not available?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260517114026.6817-1-vasant.hegde@amd.com?part=1

Re: [PATCH] x86/events/amd/iommu: Fix cpumask of IOMMU events

[Chun-Tse Shao]

Tested-by: Chun-Tse Shao <ctshao@google.com>

Thanks,
CT


On Sun, May 17, 2026 at 5:12 AM <sashiko-bot@kernel.org> wrote:
>
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [High] PMU initialization fails for IOMMUs located on NUMA nodes without online CPUs.
> --
>
> commit ef1363d0a37870d7cf1f1095cd3ebf42cc5a8bdc
> Author: Vasant Hegde <vasant.hegde@amd.com>
>
> x86/events/amd/iommu: Fix cpumask of IOMMU events
>
> This commit changes the IOMMU PMU cpumask from a single global mask to a
> per-IOMMU mask based on the NUMA node of the IOMMU, allowing per-socket
> performance counter collection.
>
> > diff --git a/arch/x86/events/amd/iommu.c b/arch/x86/events/amd/iommu.c
> > --- a/arch/x86/events/amd/iommu.c
> > +++ b/arch/x86/events/amd/iommu.c
> [ ... ]
> > @@ -440,6 +445,20 @@ static __init int init_one_iommu(unsigned int idx)
> >               return -EINVAL;
> >       }
> >
> > +     dev = amd_iommu_idx_to_dev(idx);
> > +     node = dev ? dev_to_node(dev) : NUMA_NO_NODE;
> > +     if (node != NUMA_NO_NODE)
> > +             cpu = cpumask_any_and(cpumask_of_node(node), cpu_online_mask);
>
> If the IOMMU resides on a CPU-less NUMA node (like a PCIe expansion switch
> or a memory-only CXL node), or if all CPUs on that node are currently
> offline, will cpumask_any_and() return a value greater than or equal to
> nr_cpu_ids?
>
> > +     else
> > +             cpu = cpumask_any(cpu_online_mask);
> > +
> > +     if (cpu >= nr_cpu_ids) {
> > +             pr_warn("Failed to find online CPU for IOMMU %d.\n", idx);
> > +             kfree(perf_iommu);
> > +             return -ENODEV;
> > +     }
>
> Could this cause PMU initialization to fail for IOMMUs on CPU-less nodes?
>
> Since AMD IOMMU performance counters are accessed via MMIO space, they can
> be driven by any CPU in the system. Would it be better to fall back to
> cpumask_any(cpu_online_mask) instead of returning -ENODEV when a local CPU
> is not available?
>
> --
> Sashiko AI review · https://sashiko.dev/#/patchset/20260517114026.6817-1-vasant.hegde@amd.com?part=1
>

Re: [PATCH] x86/events/amd/iommu: Fix cpumask of IOMMU events

[Vasant Hegde]

On 5/17/2026 5:42 PM, sashiko-bot@kernel.org wrote:

> 
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [High] PMU initialization fails for IOMMUs located on NUMA nodes without online CPUs.
> --
> 

Thanks for the review.

> commit ef1363d0a37870d7cf1f1095cd3ebf42cc5a8bdc
> Author: Vasant Hegde <vasant.hegde@amd.com>
> 
> x86/events/amd/iommu: Fix cpumask of IOMMU events
> 
> This commit changes the IOMMU PMU cpumask from a single global mask to a
> per-IOMMU mask based on the NUMA node of the IOMMU, allowing per-socket
> performance counter collection.
> 
>> diff --git a/arch/x86/events/amd/iommu.c b/arch/x86/events/amd/iommu.c
>> --- a/arch/x86/events/amd/iommu.c
>> +++ b/arch/x86/events/amd/iommu.c
> [ ... ]
>> @@ -440,6 +445,20 @@ static __init int init_one_iommu(unsigned int idx)
>>               return -EINVAL;
>>       }
>>
>> +     dev = amd_iommu_idx_to_dev(idx);
>> +     node = dev ? dev_to_node(dev) : NUMA_NO_NODE;
>> +     if (node != NUMA_NO_NODE)
>> +             cpu = cpumask_any_and(cpumask_of_node(node), cpu_online_mask);
> 
> If the IOMMU resides on a CPU-less NUMA node (like a PCIe expansion switch
> or a memory-only CXL node), or if all CPUs on that node are currently
> offline, will cpumask_any_and() return a value greater than or equal to
> nr_cpu_ids?

If its CPU-less then put it back to CPU 0? Any suggestions ?

-Vasant

Re: [PATCH] x86/events/amd/iommu: Fix cpumask of IOMMU events

[Jörg Rödel]

On Sun, May 17, 2026 at 11:40:26AM +0000, Vasant Hegde wrote:
> IOMMU performance counters are accessed via MMIO space. Currently IOMMU
> PMUs uses a single global cpumask (iommu_cpumask) shared across all AMD
> IOMMU PMU instances. This prevents collecting per-socket numbers
> (ex: perf stat --per-socket).
> 
> Fix this by adjusting cpumask based on IOMMUs NUMA node.
> 
> Signed-off-by: Vasant Hegde <vasant.hegde@amd.com>

Acked-by: Joerg Roedel <joerg.roedel@amd.com>

> ---
>  arch/x86/events/amd/iommu.c | 29 +++++++++++++++++++++++------
>  drivers/iommu/amd/init.c    |  7 +++++++
>  include/linux/amd-iommu.h   |  1 +
>  3 files changed, 31 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/events/amd/iommu.c b/arch/x86/events/amd/iommu.c
> index 07b110e8418a..b1848300028d 100644
> --- a/arch/x86/events/amd/iommu.c
> +++ b/arch/x86/events/amd/iommu.c
> @@ -10,6 +10,7 @@
>  
>  #define pr_fmt(fmt)	"perf/amd_iommu: " fmt
>  
> +#include <linux/device.h>
>  #include <linux/perf_event.h>
>  #include <linux/init.h>
>  #include <linux/cpumask.h>
> @@ -43,6 +44,7 @@ struct perf_amd_iommu {
>  	u8 max_counters;
>  	u64 cntr_assign_mask;
>  	raw_spinlock_t lock;
> +	cpumask_t cpumask;
>  };
>  
>  static LIST_HEAD(perf_amd_iommu_list);
> @@ -131,13 +133,15 @@ static struct amd_iommu_event_desc amd_iommu_v2_event_descs[] = {
>  /*---------------------------------------------
>   * sysfs cpumask attributes
>   *---------------------------------------------*/
> -static cpumask_t iommu_cpumask;
> -
>  static ssize_t _iommu_cpumask_show(struct device *dev,
>  				   struct device_attribute *attr,
>  				   char *buf)
>  {
> -	return cpumap_print_to_pagebuf(true, buf, &iommu_cpumask);
> +	struct pmu *pmu = dev_get_drvdata(dev);
> +	struct perf_amd_iommu *perf_iommu =
> +			container_of(pmu, struct perf_amd_iommu, pmu);
> +
> +	return cpumap_print_to_pagebuf(true, buf, &perf_iommu->cpumask);
>  }
>  static DEVICE_ATTR(cpumask, S_IRUGO, _iommu_cpumask_show, NULL);
>  
> @@ -420,7 +424,8 @@ static const struct pmu iommu_pmu __initconst = {
>  static __init int init_one_iommu(unsigned int idx)
>  {
>  	struct perf_amd_iommu *perf_iommu;
> -	int ret;
> +	struct device *dev;
> +	int node, cpu, ret;
>  
>  	perf_iommu = kzalloc_obj(struct perf_amd_iommu);
>  	if (!perf_iommu)
> @@ -440,6 +445,20 @@ static __init int init_one_iommu(unsigned int idx)
>  		return -EINVAL;
>  	}
>  
> +	dev = amd_iommu_idx_to_dev(idx);
> +	node = dev ? dev_to_node(dev) : NUMA_NO_NODE;
> +	if (node != NUMA_NO_NODE)
> +		cpu = cpumask_any_and(cpumask_of_node(node), cpu_online_mask);
> +	else
> +		cpu = cpumask_any(cpu_online_mask);
> +
> +	if (cpu >= nr_cpu_ids) {
> +		pr_warn("Failed to find online CPU for IOMMU %d.\n", idx);
> +		kfree(perf_iommu);
> +		return -ENODEV;
> +	}
> +	cpumask_set_cpu(cpu, &perf_iommu->cpumask);
> +
>  	snprintf(perf_iommu->name, IOMMU_NAME_SIZE, "amd_iommu_%u", idx);
>  
>  	ret = perf_pmu_register(&perf_iommu->pmu, perf_iommu->name, -1);
> @@ -483,8 +502,6 @@ static __init int amd_iommu_pc_init(void)
>  		return -ENODEV;
>  	}
>  
> -	/* Init cpumask attributes to only core 0 */
> -	cpumask_set_cpu(0, &iommu_cpumask);
>  	return 0;
>  }
>  
> diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
> index 3bdb380d23e9..2c35d171b5ae 100644
> --- a/drivers/iommu/amd/init.c
> +++ b/drivers/iommu/amd/init.c
> @@ -3939,6 +3939,13 @@ struct amd_iommu *get_amd_iommu(unsigned int idx)
>  	return NULL;
>  }
>  
> +struct device *amd_iommu_idx_to_dev(unsigned int idx)
> +{
> +	struct amd_iommu *iommu = get_amd_iommu(idx);
> +
> +	return iommu ? &iommu->dev->dev : NULL;
> +}
> +
>  /****************************************************************************
>   *
>   * IOMMU EFR Performance Counter support functionality. This code allows
> diff --git a/include/linux/amd-iommu.h b/include/linux/amd-iommu.h
> index edcee9f5335a..6b8d6b53b4e9 100644
> --- a/include/linux/amd-iommu.h
> +++ b/include/linux/amd-iommu.h
> @@ -67,6 +67,7 @@ int amd_iommu_pc_set_reg(struct amd_iommu *iommu, u8 bank, u8 cntr, u8 fxn,
>  int amd_iommu_pc_get_reg(struct amd_iommu *iommu, u8 bank, u8 cntr, u8 fxn,
>  		u64 *value);
>  struct amd_iommu *get_amd_iommu(unsigned int idx);
> +struct device *amd_iommu_idx_to_dev(unsigned int idx);
>  
>  #ifdef CONFIG_KVM_AMD_SEV
>  int amd_iommu_snp_disable(void);
> -- 
> 2.31.1
>