[PATCH v11 00/13] blk: honor isolcpus configuration

[PATCH v11 00/13] blk: honor isolcpus configuration

[Aaron Tomlin]

Hi,

I have decided to drive this series forward on behalf of Daniel Wagner, the
original author. This iteration addresses the outstanding architectural and
concurrency concerns raised during the previous review cycle, and the series
has been rebased on v7.0-rc5-509-g545475aebc2a.

Building upon prior iterations, this series introduces critical
architectural refinements to the mapping and affinity spreading algorithms
to guarantee thread safety and resilience against concurrent CPU-hotplug
operations. Previously, the block layer relied on a shared global static
mask (i.e., blk_hk_online_mask), which proved vulnerable to race conditions
during rapid hotplug events. This vulnerability was recently highlighted by
the kernel test robot, which encountered a NULL pointer dereference during
rcutorture (cpuhotplug) stress testing due to concurrent mask modification.

To resolve this, the architecture has been fundamentally hardened. The
global static state has been eradicated. Instead, the IRQ affinity core now
employs a newly introduced irq_spread_hk_filter(), which safely intersects
the natively calculated affinity mask with the HK_TYPE_IO_QUEUE mask.
Crucially, this is achieved using a local, hotplug-safe snapshot via
data_race(cpu_online_mask). This approach circumvents the hotplug lock
deadlocks previously identified by Thomas Gleixner, while explicitly
avoiding CONFIG_CPUMASK_OFFSTACK stack bloat hazards on high-core-count
systems. A robust fallback mechanism guarantees that should an interrupt
vector be assigned exclusively to isolated cores, it is safely re-routed to
the system's online housekeeping CPUs.

Following rigorous testing of multiple queue maps (such as NVMe poll
queues) alongside isolated CPUs, the tenth iteration resolved a critical
page fault regression. The multi-queue mapping logic has been corrected to
strictly maintain absolute hardware queue indices, ensuring faultless queue
initialisation and preventing out-of-bounds memory access.

Furthermore, following feedback from Ming Lei, the administrative
documentation for isolcpus=io_queue has undergone a comprehensive overhaul
to reflect this architectural reality. Previous iterations lacked the
required technical precision regarding subsystem impact. The expanded
kernel-parameters.txt now explicitly details that this parameter applies
strictly to managed IRQs. It thoroughly documents how the block layer
intercepts multiqueue allocation to match the housekeeping mask, actively
preventing MSI-X vector exhaustion on massive topologies and forcing queue
sharing. Most importantly, it cements the structural guarantee: while an
application on an isolated CPU may freely submit I/O, the hardware
completion interrupt is strictly and safely offloaded to a housekeeping
core.

Please let me know your thoughts.


Aaron Tomlin (1):
  genirq/affinity: Restrict managed IRQ affinity to housekeeping CPUs

Daniel Wagner (12):
  scsi: aacraid: use block layer helpers to calculate num of queues
  lib/group_cpus: remove dead !SMP code
  lib/group_cpus: Add group_mask_cpus_evenly()
  genirq/affinity: Add cpumask to struct irq_affinity
  blk-mq: add blk_mq_{online|possible}_queue_affinity
  nvme-pci: use block layer helpers to constrain queue affinity
  scsi: Use block layer helpers to constrain queue affinity
  virtio: blk/scsi: use block layer helpers to constrain queue affinity
  isolation: Introduce io_queue isolcpus type
  blk-mq: use hk cpus only when isolcpus=io_queue is enabled
  blk-mq: prevent offlining hk CPUs with associated online isolated CPUs
  docs: add io_queue flag to isolcpus

 .../admin-guide/kernel-parameters.txt         |  30 ++-
 block/blk-mq-cpumap.c                         | 192 ++++++++++++++++--
 block/blk-mq.c                                |  42 ++++
 drivers/block/virtio_blk.c                    |   4 +-
 drivers/nvme/host/pci.c                       |   1 +
 drivers/scsi/aacraid/comminit.c               |   3 +-
 drivers/scsi/hisi_sas/hisi_sas_v3_hw.c        |   1 +
 drivers/scsi/megaraid/megaraid_sas_base.c     |   5 +-
 drivers/scsi/mpi3mr/mpi3mr_fw.c               |   6 +-
 drivers/scsi/mpt3sas/mpt3sas_base.c           |   5 +-
 drivers/scsi/pm8001/pm8001_init.c             |   1 +
 drivers/scsi/virtio_scsi.c                    |   5 +-
 include/linux/blk-mq.h                        |   2 +
 include/linux/group_cpus.h                    |   3 +
 include/linux/interrupt.h                     |  16 +-
 include/linux/sched/isolation.h               |   1 +
 kernel/irq/affinity.c                         |  38 +++-
 kernel/sched/isolation.c                      |   7 +
 lib/group_cpus.c                              |  65 ++++--
 19 files changed, 379 insertions(+), 48 deletions(-)


base-commit: 3cd8b194bf3428dfa53120fee47e827a7c495815
-- 
2.51.0

[PATCH v11 01/13] scsi: aacraid: use block layer helpers to calculate num of queues

[Aaron Tomlin]

From: Daniel Wagner <wagi@kernel.org>

The calculation of the upper limit for queues does not depend solely on
the number of online CPUs; for example, the isolcpus kernel
command-line option must also be considered.

To account for this, the block layer provides a helper function to
retrieve the maximum number of queues. Use it to set an appropriate
upper queue number limit.

Fixes: 94970cfb5f10 ("scsi: use block layer helpers to calculate num of queues")
Signed-off-by: Daniel Wagner <wagi@kernel.org>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Aaron Tomlin <atomlin@atomlin.com>
---
 drivers/scsi/aacraid/comminit.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/scsi/aacraid/comminit.c b/drivers/scsi/aacraid/comminit.c
index 9bd3f5b868bc..ec165b57182d 100644
--- a/drivers/scsi/aacraid/comminit.c
+++ b/drivers/scsi/aacraid/comminit.c
@@ -469,8 +469,7 @@ void aac_define_int_mode(struct aac_dev *dev)
 	}
 
 	/* Don't bother allocating more MSI-X vectors than cpus */
-	msi_count = min(dev->max_msix,
-		(unsigned int)num_online_cpus());
+	msi_count = blk_mq_num_online_queues(dev->max_msix);
 
 	dev->max_msix = msi_count;
 
-- 
2.51.0

[PATCH v11 02/13] lib/group_cpus: remove dead !SMP code

[Aaron Tomlin]

From: Daniel Wagner <wagi@kernel.org>

The support for the !SMP configuration has been removed from the core by
commit cac5cefbade9 ("sched/smp: Make SMP unconditional").

While one can technically still compile a uniprocessor kernel, the core
scheduler now mandates SMP unconditionally, rendering this particular
!SMP fallback handling redundant. Therefore, remove the #ifdef CONFIG_SMP
guards and the fallback logic.

Signed-off-by: Daniel Wagner <wagi@kernel.org>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
[atomlin: Updated commit message to clarify !SMP removal context]
Signed-off-by: Aaron Tomlin <atomlin@atomlin.com>
---
 lib/group_cpus.c | 20 --------------------
 1 file changed, 20 deletions(-)

diff --git a/lib/group_cpus.c b/lib/group_cpus.c
index e6e18d7a49bb..b8d54398f88a 100644
--- a/lib/group_cpus.c
+++ b/lib/group_cpus.c
@@ -9,8 +9,6 @@
 #include <linux/sort.h>
 #include <linux/group_cpus.h>
 
-#ifdef CONFIG_SMP
-
 static void grp_spread_init_one(struct cpumask *irqmsk, struct cpumask *nmsk,
 				unsigned int cpus_per_grp)
 {
@@ -564,22 +562,4 @@ struct cpumask *group_cpus_evenly(unsigned int numgrps, unsigned int *nummasks)
 	*nummasks = min(nr_present + nr_others, numgrps);
 	return masks;
 }
-#else /* CONFIG_SMP */
-struct cpumask *group_cpus_evenly(unsigned int numgrps, unsigned int *nummasks)
-{
-	struct cpumask *masks;
-
-	if (numgrps == 0)
-		return NULL;
-
-	masks = kzalloc_objs(*masks, numgrps);
-	if (!masks)
-		return NULL;
-
-	/* assign all CPUs(cpu 0) to the 1st group only */
-	cpumask_copy(&masks[0], cpu_possible_mask);
-	*nummasks = 1;
-	return masks;
-}
-#endif /* CONFIG_SMP */
 EXPORT_SYMBOL_GPL(group_cpus_evenly);
-- 
2.51.0

[PATCH v11 03/13] lib/group_cpus: Add group_mask_cpus_evenly()

[Aaron Tomlin]

From: Daniel Wagner <wagi@kernel.org>

group_mask_cpu_evenly() allows the caller to pass in a CPU mask that
should be evenly distributed. This new function is a more generic
version of the existing group_cpus_evenly(), which always distributes
all present CPUs into groups.

Signed-off-by: Daniel Wagner <wagi@kernel.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Aaron Tomlin <atomlin@atomlin.com>
---
 include/linux/group_cpus.h |  3 ++
 lib/group_cpus.c           | 59 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 62 insertions(+)

diff --git a/include/linux/group_cpus.h b/include/linux/group_cpus.h
index 9d4e5ab6c314..defab4123a82 100644
--- a/include/linux/group_cpus.h
+++ b/include/linux/group_cpus.h
@@ -10,5 +10,8 @@
 #include <linux/cpu.h>
 
 struct cpumask *group_cpus_evenly(unsigned int numgrps, unsigned int *nummasks);
+struct cpumask *group_mask_cpus_evenly(unsigned int numgrps,
+				       const struct cpumask *mask,
+				       unsigned int *nummasks);
 
 #endif
diff --git a/lib/group_cpus.c b/lib/group_cpus.c
index b8d54398f88a..d3e9a20250ff 100644
--- a/lib/group_cpus.c
+++ b/lib/group_cpus.c
@@ -8,6 +8,7 @@
 #include <linux/cpu.h>
 #include <linux/sort.h>
 #include <linux/group_cpus.h>
+#include <linux/sched/isolation.h>
 
 static void grp_spread_init_one(struct cpumask *irqmsk, struct cpumask *nmsk,
 				unsigned int cpus_per_grp)
@@ -563,3 +564,61 @@ struct cpumask *group_cpus_evenly(unsigned int numgrps, unsigned int *nummasks)
 	return masks;
 }
 EXPORT_SYMBOL_GPL(group_cpus_evenly);
+
+/**
+ * group_mask_cpus_evenly - Group all CPUs evenly per NUMA/CPU locality
+ * @numgrps: number of cpumasks to create
+ * @mask: CPUs to consider for the grouping
+ * @nummasks: number of initialized cpusmasks
+ *
+ * Return: cpumask array if successful, NULL otherwise. Only the CPUs
+ * marked in the mask will be considered for the grouping. And each
+ * element includes CPUs assigned to this group. nummasks contains the
+ * number of initialized masks which can be less than numgrps. cpu_mask
+ *
+ * Try to put close CPUs from viewpoint of CPU and NUMA locality into
+ * same group, and run two-stage grouping:
+ *	1) allocate present CPUs on these groups evenly first
+ *	2) allocate other possible CPUs on these groups evenly
+ *
+ * We guarantee in the resulted grouping that all CPUs are covered, and
+ * no same CPU is assigned to multiple groups
+ */
+struct cpumask *group_mask_cpus_evenly(unsigned int numgrps,
+				       const struct cpumask *mask,
+				       unsigned int *nummasks)
+{
+	cpumask_var_t *node_to_cpumask;
+	cpumask_var_t nmsk;
+	int ret = -ENOMEM;
+	struct cpumask *masks = NULL;
+
+	if (!zalloc_cpumask_var(&nmsk, GFP_KERNEL))
+		return NULL;
+
+	node_to_cpumask = alloc_node_to_cpumask();
+	if (!node_to_cpumask)
+		goto fail_nmsk;
+
+	masks = kcalloc(numgrps, sizeof(*masks), GFP_KERNEL);
+	if (!masks)
+		goto fail_node_to_cpumask;
+
+	build_node_to_cpumask(node_to_cpumask);
+
+	ret = __group_cpus_evenly(0, numgrps, node_to_cpumask, mask, nmsk,
+				  masks);
+
+fail_node_to_cpumask:
+	free_node_to_cpumask(node_to_cpumask);
+
+fail_nmsk:
+	free_cpumask_var(nmsk);
+	if (ret < 0) {
+		kfree(masks);
+		return NULL;
+	}
+	*nummasks = ret;
+	return masks;
+}
+EXPORT_SYMBOL_GPL(group_mask_cpus_evenly);
-- 
2.51.0

[PATCH v11 04/13] genirq/affinity: Add cpumask to struct irq_affinity

[Aaron Tomlin]

From: Daniel Wagner <wagi@kernel.org>

Pass a cpumask to irq_create_affinity_masks as an additional constraint
to consider when creating the affinity masks. This allows the caller to
exclude specific CPUs, e.g., isolated CPUs (see the 'isolcpus' kernel
command-line parameter).

Signed-off-by: Daniel Wagner <wagi@kernel.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Aaron Tomlin <atomlin@atomlin.com>
---
 include/linux/interrupt.h | 16 ++++++++++------
 kernel/irq/affinity.c     | 12 ++++++++++--
 2 files changed, 20 insertions(+), 8 deletions(-)

diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
index 6cd26ffb0505..afd5a2c75b43 100644
--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -287,18 +287,22 @@ struct irq_affinity_notify {
  * @nr_sets:		The number of interrupt sets for which affinity
  *			spreading is required
  * @set_size:		Array holding the size of each interrupt set
+ * @mask:		cpumask that constrains which CPUs to consider when
+ *			calculating the number and size of the interrupt sets
  * @calc_sets:		Callback for calculating the number and size
  *			of interrupt sets
  * @priv:		Private data for usage by @calc_sets, usually a
  *			pointer to driver/device specific data.
  */
 struct irq_affinity {
-	unsigned int	pre_vectors;
-	unsigned int	post_vectors;
-	unsigned int	nr_sets;
-	unsigned int	set_size[IRQ_AFFINITY_MAX_SETS];
-	void		(*calc_sets)(struct irq_affinity *, unsigned int nvecs);
-	void		*priv;
+	unsigned int		pre_vectors;
+	unsigned int		post_vectors;
+	unsigned int		nr_sets;
+	unsigned int		set_size[IRQ_AFFINITY_MAX_SETS];
+	const struct cpumask	*mask;
+	void			(*calc_sets)(struct irq_affinity *,
+					     unsigned int nvecs);
+	void			*priv;
 };
 
 /**
diff --git a/kernel/irq/affinity.c b/kernel/irq/affinity.c
index 78f2418a8925..e0cf70a99339 100644
--- a/kernel/irq/affinity.c
+++ b/kernel/irq/affinity.c
@@ -70,7 +70,13 @@ irq_create_affinity_masks(unsigned int nvecs, struct irq_affinity *affd)
 	 */
 	for (i = 0, usedvecs = 0; i < affd->nr_sets; i++) {
 		unsigned int nr_masks, this_vecs = affd->set_size[i];
-		struct cpumask *result = group_cpus_evenly(this_vecs, &nr_masks);
+		struct cpumask *result;
+
+		if (affd->mask)
+			result = group_mask_cpus_evenly(this_vecs, affd->mask,
+							&nr_masks);
+		else
+			result = group_cpus_evenly(this_vecs, &nr_masks);
 
 		if (!result) {
 			kfree(masks);
@@ -115,7 +121,9 @@ unsigned int irq_calc_affinity_vectors(unsigned int minvec, unsigned int maxvec,
 	if (resv > minvec)
 		return 0;
 
-	if (affd->calc_sets)
+	if (affd->mask)
+		set_vecs = cpumask_weight(affd->mask);
+	else if (affd->calc_sets)
 		set_vecs = maxvec - resv;
 	else
 		set_vecs = cpumask_weight(cpu_possible_mask);
-- 
2.51.0

[PATCH v11 05/13] blk-mq: add blk_mq_{online|possible}_queue_affinity

[Aaron Tomlin]

From: Daniel Wagner <wagi@kernel.org>

Introduce blk_mq_{online|possible}_queue_affinity, which returns the
queue-to-CPU mapping constraints defined by the block layer. This allows
other subsystems (e.g., IRQ affinity setup) to respect block layer
requirements.

It is necessary to provide versions for both the online and possible CPU
masks because some drivers want to spread their I/O queues only across
online CPUs, while others prefer to use all possible CPUs. And the mask
used needs to match with the number of queues requested
(see blk_num_{online|possible}_queues).

Signed-off-by: Daniel Wagner <wagi@kernel.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Aaron Tomlin <atomlin@atomlin.com>
---
 block/blk-mq-cpumap.c  | 24 ++++++++++++++++++++++++
 include/linux/blk-mq.h |  2 ++
 2 files changed, 26 insertions(+)

diff --git a/block/blk-mq-cpumap.c b/block/blk-mq-cpumap.c
index 705da074ad6c..8244ecf87835 100644
--- a/block/blk-mq-cpumap.c
+++ b/block/blk-mq-cpumap.c
@@ -26,6 +26,30 @@ static unsigned int blk_mq_num_queues(const struct cpumask *mask,
 	return min_not_zero(num, max_queues);
 }
 
+/**
+ * blk_mq_possible_queue_affinity - Return block layer queue affinity
+ *
+ * Returns an affinity mask that represents the queue-to-CPU mapping
+ * requested by the block layer based on possible CPUs.
+ */
+const struct cpumask *blk_mq_possible_queue_affinity(void)
+{
+	return cpu_possible_mask;
+}
+EXPORT_SYMBOL_GPL(blk_mq_possible_queue_affinity);
+
+/**
+ * blk_mq_online_queue_affinity - Return block layer queue affinity
+ *
+ * Returns an affinity mask that represents the queue-to-CPU mapping
+ * requested by the block layer based on online CPUs.
+ */
+const struct cpumask *blk_mq_online_queue_affinity(void)
+{
+	return cpu_online_mask;
+}
+EXPORT_SYMBOL_GPL(blk_mq_online_queue_affinity);
+
 /**
  * blk_mq_num_possible_queues - Calc nr of queues for multiqueue devices
  * @max_queues:	The maximum number of queues the hardware/driver
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 18a2388ba581..ebc45557aee8 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -969,6 +969,8 @@ int blk_mq_freeze_queue_wait_timeout(struct request_queue *q,
 void blk_mq_unfreeze_queue_non_owner(struct request_queue *q);
 void blk_freeze_queue_start_non_owner(struct request_queue *q);
 
+const struct cpumask *blk_mq_possible_queue_affinity(void);
+const struct cpumask *blk_mq_online_queue_affinity(void);
 unsigned int blk_mq_num_possible_queues(unsigned int max_queues);
 unsigned int blk_mq_num_online_queues(unsigned int max_queues);
 void blk_mq_map_queues(struct blk_mq_queue_map *qmap);
-- 
2.51.0

[PATCH v11 06/13] nvme-pci: use block layer helpers to constrain queue affinity

[Aaron Tomlin]

From: Daniel Wagner <wagi@kernel.org>

Ensure that IRQ affinity setup also respects the queue-to-CPU mapping
constraints provided by the block layer. This allows the NVMe driver
to avoid assigning interrupts to CPUs that the block layer has excluded
(e.g., isolated CPUs).

Signed-off-by: Daniel Wagner <wagi@kernel.org>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Aaron Tomlin <atomlin@atomlin.com>
---
 drivers/nvme/host/pci.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index db5fc9bf6627..daa041d15d3c 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -2862,6 +2862,7 @@ static int nvme_setup_irqs(struct nvme_dev *dev, unsigned int nr_io_queues)
 		.pre_vectors	= 1,
 		.calc_sets	= nvme_calc_irq_sets,
 		.priv		= dev,
+		.mask		= blk_mq_possible_queue_affinity(),
 	};
 	unsigned int irq_queues, poll_queues;
 	unsigned int flags = PCI_IRQ_ALL_TYPES | PCI_IRQ_AFFINITY;
-- 
2.51.0

[PATCH v11 07/13] scsi: Use block layer helpers to constrain queue affinity

[Aaron Tomlin]

From: Daniel Wagner <wagi@kernel.org>

Ensure that IRQ affinity setup also respects the queue-to-CPU mapping
constraints provided by the block layer. This allows the SCSI drivers
to avoid assigning interrupts to CPUs that the block layer has excluded
(e.g., isolated CPUs).

Only convert drivers which are already using the
pci_alloc_irq_vectors_affinity with the PCI_IRQ_AFFINITY flag set.
Because these drivers are enabled to let the IRQ core code to
set the affinity. Also don't update qla2xxx because the nvme-fabrics
code is not ready yet.

Signed-off-by: Daniel Wagner <wagi@kernel.org>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Aaron Tomlin <atomlin@atomlin.com>
---
 drivers/scsi/hisi_sas/hisi_sas_v3_hw.c    | 1 +
 drivers/scsi/megaraid/megaraid_sas_base.c | 5 ++++-
 drivers/scsi/mpi3mr/mpi3mr_fw.c           | 6 +++++-
 drivers/scsi/mpt3sas/mpt3sas_base.c       | 5 ++++-
 drivers/scsi/pm8001/pm8001_init.c         | 1 +
 5 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/drivers/scsi/hisi_sas/hisi_sas_v3_hw.c b/drivers/scsi/hisi_sas/hisi_sas_v3_hw.c
index f69efc6494b8..d1f689224e7b 100644
--- a/drivers/scsi/hisi_sas/hisi_sas_v3_hw.c
+++ b/drivers/scsi/hisi_sas/hisi_sas_v3_hw.c
@@ -2605,6 +2605,7 @@ static int interrupt_preinit_v3_hw(struct hisi_hba *hisi_hba)
 	struct pci_dev *pdev = hisi_hba->pci_dev;
 	struct irq_affinity desc = {
 		.pre_vectors = BASE_VECTORS_V3_HW,
+		.mask = blk_mq_online_queue_affinity(),
 	};
 
 	min_msi = MIN_AFFINE_VECTORS_V3_HW;
diff --git a/drivers/scsi/megaraid/megaraid_sas_base.c b/drivers/scsi/megaraid/megaraid_sas_base.c
index ac71ea4898b2..7e2a3c187ee0 100644
--- a/drivers/scsi/megaraid/megaraid_sas_base.c
+++ b/drivers/scsi/megaraid/megaraid_sas_base.c
@@ -5925,7 +5925,10 @@ static int
 __megasas_alloc_irq_vectors(struct megasas_instance *instance)
 {
 	int i, irq_flags;
-	struct irq_affinity desc = { .pre_vectors = instance->low_latency_index_start };
+	struct irq_affinity desc = {
+		.pre_vectors = instance->low_latency_index_start,
+		.mask = blk_mq_online_queue_affinity(),
+	};
 	struct irq_affinity *descp = &desc;
 
 	irq_flags = PCI_IRQ_MSIX;
diff --git a/drivers/scsi/mpi3mr/mpi3mr_fw.c b/drivers/scsi/mpi3mr/mpi3mr_fw.c
index c744210cc901..f9b8b3639c64 100644
--- a/drivers/scsi/mpi3mr/mpi3mr_fw.c
+++ b/drivers/scsi/mpi3mr/mpi3mr_fw.c
@@ -830,7 +830,11 @@ static int mpi3mr_setup_isr(struct mpi3mr_ioc *mrioc, u8 setup_one)
 	int max_vectors, min_vec;
 	int retval;
 	int i;
-	struct irq_affinity desc = { .pre_vectors =  1, .post_vectors = 1 };
+	struct irq_affinity desc = {
+		.pre_vectors =  1,
+		.post_vectors = 1,
+		.mask = blk_mq_online_queue_affinity(),
+	};
 
 	if (mrioc->is_intr_info_set)
 		return 0;
diff --git a/drivers/scsi/mpt3sas/mpt3sas_base.c b/drivers/scsi/mpt3sas/mpt3sas_base.c
index 79052f2accbd..91e1622b5b77 100644
--- a/drivers/scsi/mpt3sas/mpt3sas_base.c
+++ b/drivers/scsi/mpt3sas/mpt3sas_base.c
@@ -3370,7 +3370,10 @@ static int
 _base_alloc_irq_vectors(struct MPT3SAS_ADAPTER *ioc)
 {
 	int i, irq_flags = PCI_IRQ_MSIX;
-	struct irq_affinity desc = { .pre_vectors = ioc->high_iops_queues };
+	struct irq_affinity desc = {
+		.pre_vectors = ioc->high_iops_queues,
+		.mask = blk_mq_online_queue_affinity(),
+	};
 	struct irq_affinity *descp = &desc;
 	/*
 	 * Don't allocate msix vectors for poll_queues.
diff --git a/drivers/scsi/pm8001/pm8001_init.c b/drivers/scsi/pm8001/pm8001_init.c
index e93ea76b565e..6360fa95bcf4 100644
--- a/drivers/scsi/pm8001/pm8001_init.c
+++ b/drivers/scsi/pm8001/pm8001_init.c
@@ -978,6 +978,7 @@ static u32 pm8001_setup_msix(struct pm8001_hba_info *pm8001_ha)
 		 */
 		struct irq_affinity desc = {
 			.pre_vectors = 1,
+			.mask = blk_mq_online_queue_affinity(),
 		};
 		rc = pci_alloc_irq_vectors_affinity(
 				pm8001_ha->pdev, 2, PM8001_MAX_MSIX_VEC,
-- 
2.51.0

[PATCH v11 08/13] virtio: blk/scsi: use block layer helpers to constrain queue affinity

[Aaron Tomlin]

From: Daniel Wagner <wagi@kernel.org>

Ensure that IRQ affinity setup also respects the queue-to-CPU mapping
constraints provided by the block layer. This allows the virtio drivers
to avoid assigning interrupts to CPUs that the block layer has excluded
(e.g., isolated CPUs).

Signed-off-by: Daniel Wagner <wagi@kernel.org>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Aaron Tomlin <atomlin@atomlin.com>
---
 drivers/block/virtio_blk.c | 4 +++-
 drivers/scsi/virtio_scsi.c | 5 ++++-
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index b1c9a27fe00f..9d737510454b 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -964,7 +964,9 @@ static int init_vq(struct virtio_blk *vblk)
 	unsigned short num_vqs;
 	unsigned short num_poll_vqs;
 	struct virtio_device *vdev = vblk->vdev;
-	struct irq_affinity desc = { 0, };
+	struct irq_affinity desc = {
+		.mask = blk_mq_possible_queue_affinity(),
+	};
 
 	err = virtio_cread_feature(vdev, VIRTIO_BLK_F_MQ,
 				   struct virtio_blk_config, num_queues,
diff --git a/drivers/scsi/virtio_scsi.c b/drivers/scsi/virtio_scsi.c
index 0ed8558dad72..520a7da5386e 100644
--- a/drivers/scsi/virtio_scsi.c
+++ b/drivers/scsi/virtio_scsi.c
@@ -849,7 +849,10 @@ static int virtscsi_init(struct virtio_device *vdev,
 	u32 num_vqs, num_poll_vqs, num_req_vqs;
 	struct virtqueue_info *vqs_info;
 	struct virtqueue **vqs;
-	struct irq_affinity desc = { .pre_vectors = 2 };
+	struct irq_affinity desc = {
+		.pre_vectors = 2,
+		.mask = blk_mq_possible_queue_affinity(),
+	};
 
 	num_req_vqs = vscsi->num_queues;
 	num_vqs = num_req_vqs + VIRTIO_SCSI_VQ_BASE;
-- 
2.51.0

[PATCH v11 09/13] isolation: Introduce io_queue isolcpus type

[Aaron Tomlin]

From: Daniel Wagner <wagi@kernel.org>

Multiqueue drivers spread I/O queues across all CPUs for optimal
performance. However, these drivers are not aware of CPU isolation
requirements and will distribute queues without considering the isolcpus
configuration.

Introduce a new isolcpus mask that allows users to define which CPUs
should have I/O queues assigned. This is similar to managed_irq, but
intended for drivers that do not use the managed IRQ infrastructure

Signed-off-by: Daniel Wagner <wagi@kernel.org>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Aaron Tomlin <atomlin@atomlin.com>
---
 include/linux/sched/isolation.h | 1 +
 kernel/sched/isolation.c        | 7 +++++++
 2 files changed, 8 insertions(+)

diff --git a/include/linux/sched/isolation.h b/include/linux/sched/isolation.h
index dc3975ff1b2e..7b266fc2a405 100644
--- a/include/linux/sched/isolation.h
+++ b/include/linux/sched/isolation.h
@@ -18,6 +18,7 @@ enum hk_type {
 	HK_TYPE_MANAGED_IRQ,
 	/* Inverse of boot-time nohz_full= or isolcpus=nohz arguments */
 	HK_TYPE_KERNEL_NOISE,
+	HK_TYPE_IO_QUEUE,
 	HK_TYPE_MAX,
 
 	/*
diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
index ef152d401fe2..3406e3024fd4 100644
--- a/kernel/sched/isolation.c
+++ b/kernel/sched/isolation.c
@@ -16,6 +16,7 @@ enum hk_flags {
 	HK_FLAG_DOMAIN		= BIT(HK_TYPE_DOMAIN),
 	HK_FLAG_MANAGED_IRQ	= BIT(HK_TYPE_MANAGED_IRQ),
 	HK_FLAG_KERNEL_NOISE	= BIT(HK_TYPE_KERNEL_NOISE),
+	HK_FLAG_IO_QUEUE	= BIT(HK_TYPE_IO_QUEUE),
 };
 
 DEFINE_STATIC_KEY_FALSE(housekeeping_overridden);
@@ -340,6 +341,12 @@ static int __init housekeeping_isolcpus_setup(char *str)
 			continue;
 		}
 
+		if (!strncmp(str, "io_queue,", 9)) {
+			str += 9;
+			flags |= HK_FLAG_IO_QUEUE;
+			continue;
+		}
+
 		/*
 		 * Skip unknown sub-parameter and validate that it is not
 		 * containing an invalid character.
-- 
2.51.0

[PATCH v11 10/13] blk-mq: use hk cpus only when isolcpus=io_queue is enabled

[Aaron Tomlin]

From: Daniel Wagner <wagi@kernel.org>

Extend the capabilities of the generic CPU to hardware queue (hctx)
mapping code, so it maps houskeeping CPUs and isolated CPUs to the
hardware queues evenly.

A hctx is only operational when there is at least one online
housekeeping CPU assigned (aka active_hctx). Thus, check the final
mapping that there is no hctx which has only offline housekeeing CPU and
online isolated CPUs.

Example mapping result:

  16 online CPUs

  isolcpus=io_queue,2-3,6-7,12-13

Queue mapping:
        hctx0: default 0 2
        hctx1: default 1 3
        hctx2: default 4 6
        hctx3: default 5 7
        hctx4: default 8 12
        hctx5: default 9 13
        hctx6: default 10
        hctx7: default 11
        hctx8: default 14
        hctx9: default 15

IRQ mapping:
        irq 42 affinity 0 effective 0  nvme0q0
        irq 43 affinity 0 effective 0  nvme0q1
        irq 44 affinity 1 effective 1  nvme0q2
        irq 45 affinity 4 effective 4  nvme0q3
        irq 46 affinity 5 effective 5  nvme0q4
        irq 47 affinity 8 effective 8  nvme0q5
        irq 48 affinity 9 effective 9  nvme0q6
        irq 49 affinity 10 effective 10  nvme0q7
        irq 50 affinity 11 effective 11  nvme0q8
        irq 51 affinity 14 effective 14  nvme0q9
        irq 52 affinity 15 effective 15  nvme0q10

A corner case is when the number of online CPUs and present CPUs
differ and the driver asks for less queues than online CPUs, e.g.

  8 online CPUs, 16 possible CPUs

  isolcpus=io_queue,2-3,6-7,12-13
  virtio_blk.num_request_queues=2

Queue mapping:
        hctx0: default 0 1 2 3 4 5 6 7 8 12 13
        hctx1: default 9 10 11 14 15

IRQ mapping
        irq 27 affinity 0 effective 0 virtio0-config
        irq 28 affinity 0-1,4-5,8 effective 5 virtio0-req.0
        irq 29 affinity 9-11,14-15 effective 0 virtio0-req.1

Noteworthy is that for the normal/default configuration (!isoclpus) the
mapping will change for systems which have non hyperthreading CPUs. The
main assignment loop will completely rely that group_mask_cpus_evenly to
do the right thing. The old code would distribute the CPUs linearly over
the hardware context:

queue mapping for /dev/nvme0n1
        hctx0: default 0 8
        hctx1: default 1 9
        hctx2: default 2 10
        hctx3: default 3 11
        hctx4: default 4 12
        hctx5: default 5 13
        hctx6: default 6 14
        hctx7: default 7 15

The assign each hardware context the map generated by the
group_mask_cpus_evenly function:

queue mapping for /dev/nvme0n1
        hctx0: default 0 1
        hctx1: default 2 3
        hctx2: default 4 5
        hctx3: default 6 7
        hctx4: default 8 9
        hctx5: default 10 11
        hctx6: default 12 13
        hctx7: default 14 15

In case of hyperthreading CPUs, the resulting map stays the same.

Signed-off-by: Daniel Wagner <wagi@kernel.org>
[atomlin:
    - Fixed absolute vs. relative hardware queue index mix-up in
      blk_mq_map_queues and validation checks; fixed typographical
      errors
    - Reduced stack frame size of blk_mq_num_queues()]
Signed-off-by: Aaron Tomlin <atomlin@atomlin.com>
---
 block/blk-mq-cpumap.c | 168 +++++++++++++++++++++++++++++++++++++-----
 1 file changed, 150 insertions(+), 18 deletions(-)

diff --git a/block/blk-mq-cpumap.c b/block/blk-mq-cpumap.c
index 8244ecf87835..f7c5f52f3b35 100644
--- a/block/blk-mq-cpumap.c
+++ b/block/blk-mq-cpumap.c
@@ -22,7 +22,11 @@ static unsigned int blk_mq_num_queues(const struct cpumask *mask,
 {
 	unsigned int num;
 
-	num = cpumask_weight(mask);
+	if (housekeeping_enabled(HK_TYPE_IO_QUEUE))
+		num = cpumask_weight_and(mask, housekeeping_cpumask(HK_TYPE_IO_QUEUE));
+	else
+		num = cpumask_weight(mask);
+
 	return min_not_zero(num, max_queues);
 }
 
@@ -31,9 +35,13 @@ static unsigned int blk_mq_num_queues(const struct cpumask *mask,
  *
  * Returns an affinity mask that represents the queue-to-CPU mapping
  * requested by the block layer based on possible CPUs.
+ * This helper takes isolcpus settings into account.
  */
 const struct cpumask *blk_mq_possible_queue_affinity(void)
 {
+	if (housekeeping_enabled(HK_TYPE_IO_QUEUE))
+		return housekeeping_cpumask(HK_TYPE_IO_QUEUE);
+
 	return cpu_possible_mask;
 }
 EXPORT_SYMBOL_GPL(blk_mq_possible_queue_affinity);
@@ -46,6 +54,14 @@ EXPORT_SYMBOL_GPL(blk_mq_possible_queue_affinity);
  */
 const struct cpumask *blk_mq_online_queue_affinity(void)
 {
+	/*
+	 * Return the stable housekeeping mask if enabled. Callers (e.g.,
+	 * the IRQ affinity core) are responsible for safely intersecting
+	 * this with a local snapshot of the online mask.
+	 */
+	if (housekeeping_enabled(HK_TYPE_IO_QUEUE))
+		return housekeeping_cpumask(HK_TYPE_IO_QUEUE);
+
 	return cpu_online_mask;
 }
 EXPORT_SYMBOL_GPL(blk_mq_online_queue_affinity);
@@ -57,7 +73,8 @@ EXPORT_SYMBOL_GPL(blk_mq_online_queue_affinity);
  *		ignored.
  *
  * Calculates the number of queues to be used for a multiqueue
- * device based on the number of possible CPUs.
+ * device based on the number of possible CPUs. This helper
+ * takes isolcpus settings into account.
  */
 unsigned int blk_mq_num_possible_queues(unsigned int max_queues)
 {
@@ -72,7 +89,8 @@ EXPORT_SYMBOL_GPL(blk_mq_num_possible_queues);
  *		ignored.
  *
  * Calculates the number of queues to be used for a multiqueue
- * device based on the number of online CPUs.
+ * device based on the number of online CPUs. This helper
+ * takes isolcpus settings into account.
  */
 unsigned int blk_mq_num_online_queues(unsigned int max_queues)
 {
@@ -80,23 +98,104 @@ unsigned int blk_mq_num_online_queues(unsigned int max_queues)
 }
 EXPORT_SYMBOL_GPL(blk_mq_num_online_queues);
 
+static bool blk_mq_validate(struct blk_mq_queue_map *qmap,
+			    const struct cpumask *active_hctx)
+{
+	/*
+	 * Verify if the mapping is usable when housekeeping
+	 * configuration is enabled
+	 */
+
+	for (int queue = 0; queue < qmap->nr_queues; queue++) {
+		int cpu;
+
+		if (cpumask_test_cpu(queue, active_hctx)) {
+			/*
+			 * This hctx has at least one online CPU thus it
+			 * is able to serve any assigned isolated CPU.
+			 */
+			continue;
+		}
+
+		/*
+		 * There is no housekeeping online CPU for this hctx, all
+		 * good as long as all non-housekeeping CPUs are also
+		 * offline.
+		 */
+		for_each_online_cpu(cpu) {
+			if (qmap->mq_map[cpu] != qmap->queue_offset + queue)
+				continue;
+
+			pr_warn("Unable to create a usable CPU-to-queue mapping with the given constraints\n");
+			return false;
+		}
+	}
+
+	return true;
+}
+
+static void blk_mq_map_fallback(struct blk_mq_queue_map *qmap)
+{
+	unsigned int cpu;
+
+	/*
+	 * Map all CPUs to the first hctx to ensure at least one online
+	 * CPU is serving it.
+	 */
+	for_each_possible_cpu(cpu)
+		qmap->mq_map[cpu] = 0;
+}
+
 void blk_mq_map_queues(struct blk_mq_queue_map *qmap)
 {
-	const struct cpumask *masks;
+	struct cpumask *masks __free(kfree) = NULL;
+	const struct cpumask *constraint;
 	unsigned int queue, cpu, nr_masks;
+	cpumask_var_t active_hctx;
 
-	masks = group_cpus_evenly(qmap->nr_queues, &nr_masks);
-	if (!masks) {
-		for_each_possible_cpu(cpu)
-			qmap->mq_map[cpu] = qmap->queue_offset;
-		return;
-	}
+	if (!zalloc_cpumask_var(&active_hctx, GFP_KERNEL))
+		goto fallback;
+
+	if (housekeeping_enabled(HK_TYPE_IO_QUEUE))
+		constraint = housekeeping_cpumask(HK_TYPE_IO_QUEUE);
+	else
+		constraint = cpu_possible_mask;
+
+	/* Map CPUs to the hardware contexts (hctx) */
+	masks = group_mask_cpus_evenly(qmap->nr_queues, constraint, &nr_masks);
+	if (!masks)
+		goto free_fallback;
 
 	for (queue = 0; queue < qmap->nr_queues; queue++) {
-		for_each_cpu(cpu, &masks[queue % nr_masks])
+		unsigned int idx = (qmap->queue_offset + queue) % nr_masks;
+
+		for_each_cpu(cpu, &masks[idx]) {
 			qmap->mq_map[cpu] = qmap->queue_offset + queue;
+
+			if (cpu_online(cpu))
+				cpumask_set_cpu(queue, active_hctx);
+		}
 	}
-	kfree(masks);
+
+	/* Map any unassigned CPU evenly to the hardware contexts (hctx) */
+	queue = cpumask_first(active_hctx);
+	for_each_cpu_andnot(cpu, cpu_possible_mask, constraint) {
+		qmap->mq_map[cpu] = qmap->queue_offset + queue;
+		queue = cpumask_next_wrap(queue, active_hctx);
+	}
+
+	if (!blk_mq_validate(qmap, active_hctx))
+		goto free_fallback;
+
+	free_cpumask_var(active_hctx);
+
+	return;
+
+free_fallback:
+	free_cpumask_var(active_hctx);
+
+fallback:
+	blk_mq_map_fallback(qmap);
 }
 EXPORT_SYMBOL_GPL(blk_mq_map_queues);
 
@@ -133,24 +232,57 @@ void blk_mq_map_hw_queues(struct blk_mq_queue_map *qmap,
 			  struct device *dev, unsigned int offset)
 
 {
-	const struct cpumask *mask;
+	cpumask_var_t active_hctx, mask;
 	unsigned int queue, cpu;
 
 	if (!dev->bus->irq_get_affinity)
 		goto fallback;
 
+	if (!zalloc_cpumask_var(&active_hctx, GFP_KERNEL))
+		goto fallback;
+
+	if (!zalloc_cpumask_var(&mask, GFP_KERNEL)) {
+		free_cpumask_var(active_hctx);
+		goto fallback;
+	}
+
+	/* Map CPUs to the hardware contexts (hctx) */
 	for (queue = 0; queue < qmap->nr_queues; queue++) {
-		mask = dev->bus->irq_get_affinity(dev, queue + offset);
-		if (!mask)
-			goto fallback;
+		const struct cpumask *affinity_mask;
 
-		for_each_cpu(cpu, mask)
+		affinity_mask = dev->bus->irq_get_affinity(dev, offset + queue);
+		if (!affinity_mask)
+			goto free_fallback;
+
+		for_each_cpu(cpu, affinity_mask) {
 			qmap->mq_map[cpu] = qmap->queue_offset + queue;
+
+			cpumask_set_cpu(cpu, mask);
+			if (cpu_online(cpu))
+				cpumask_set_cpu(queue, active_hctx);
+		}
 	}
 
+	/* Map any unassigned CPU evenly to the hardware contexts (hctx) */
+	queue = cpumask_first(active_hctx);
+	for_each_cpu_andnot(cpu, cpu_possible_mask, mask) {
+		qmap->mq_map[cpu] = qmap->queue_offset + queue;
+		queue = cpumask_next_wrap(queue, active_hctx);
+	}
+
+	if (!blk_mq_validate(qmap, active_hctx))
+		goto free_fallback;
+
+	free_cpumask_var(active_hctx);
+	free_cpumask_var(mask);
+
 	return;
 
+free_fallback:
+	free_cpumask_var(active_hctx);
+	free_cpumask_var(mask);
+
 fallback:
-	blk_mq_map_queues(qmap);
+	blk_mq_map_fallback(qmap);
 }
 EXPORT_SYMBOL_GPL(blk_mq_map_hw_queues);
-- 
2.51.0

[PATCH v11 11/13] blk-mq: prevent offlining hk CPUs with associated online isolated CPUs

[Aaron Tomlin]

From: Daniel Wagner <wagi@kernel.org>

When isolcpus=io_queue is enabled, and the last housekeeping CPU for a
given hctx goes offline, there would be no CPU left to handle I/O. To
prevent I/O stalls, prevent offlining housekeeping CPUs that are still
serving isolated CPUs.

When isolcpus=io_queue is enabled and the last housekeeping CPU
for a given hctx goes offline, no CPU would be left to handle I/O.
To prevent I/O stalls, disallow offlining housekeeping CPUs that are
still serving isolated CPUs.

Signed-off-by: Daniel Wagner <wagi@kernel.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Aaron Tomlin <atomlin@atomlin.com>
---
 block/blk-mq.c | 42 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 4c5c16cce4f8..4257d5b26641 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -3720,6 +3720,43 @@ static bool blk_mq_hctx_has_requests(struct blk_mq_hw_ctx *hctx)
 	return data.has_rq;
 }
 
+static bool blk_mq_hctx_can_offline_hk_cpu(struct blk_mq_hw_ctx *hctx,
+					   unsigned int this_cpu)
+{
+	const struct cpumask *hk_mask = housekeeping_cpumask(HK_TYPE_IO_QUEUE);
+
+	for (int i = 0; i < hctx->nr_ctx; i++) {
+		struct blk_mq_ctx *ctx = hctx->ctxs[i];
+
+		if (ctx->cpu == this_cpu)
+			continue;
+
+		/*
+		 * Check if this context has at least one online
+		 * housekeeping CPU; in this case the hardware context is
+		 * usable.
+		 */
+		if (cpumask_test_cpu(ctx->cpu, hk_mask) &&
+		    cpu_online(ctx->cpu))
+			break;
+
+		/*
+		 * The context doesn't have any online housekeeping CPUs,
+		 * but there might be an online isolated CPU mapped to
+		 * it.
+		 */
+		if (cpu_is_offline(ctx->cpu))
+			continue;
+
+		pr_warn("%s: trying to offline hctx%d but there is still an online isolcpu CPU %d mapped to it\n",
+			hctx->queue->disk->disk_name,
+			hctx->queue_num, ctx->cpu);
+		return false;
+	}
+
+	return true;
+}
+
 static bool blk_mq_hctx_has_online_cpu(struct blk_mq_hw_ctx *hctx,
 		unsigned int this_cpu)
 {
@@ -3752,6 +3789,11 @@ static int blk_mq_hctx_notify_offline(unsigned int cpu, struct hlist_node *node)
 			struct blk_mq_hw_ctx, cpuhp_online);
 	int ret = 0;
 
+	if (housekeeping_enabled(HK_TYPE_IO_QUEUE)) {
+		if (!blk_mq_hctx_can_offline_hk_cpu(hctx, cpu))
+			return -EINVAL;
+	}
+
 	if (!hctx->nr_ctx || blk_mq_hctx_has_online_cpu(hctx, cpu))
 		return 0;
 
-- 
2.51.0

Re: [PATCH v11 11/13] blk-mq: prevent offlining hk CPUs with associated online isolated CPUs

[Marco Crivellari]

Hi,

Seems like the commit log of this patch is duplicated, isn't it?
I noticed it's like this from v7.

Thanks!

--

Marco Crivellari

SUSE Labs

Re: [PATCH v11 11/13] blk-mq: prevent offlining hk CPUs with associated online isolated CPUs

[Aaron Tomlin]

[-- Attachment #1: Type: text/plain, Size: 304 bytes --]

On Fri, Apr 17, 2026 at 06:11:16PM +0200, Marco Crivellari wrote:
> Hi,
> 
> Seems like the commit log of this patch is duplicated, isn't it?
> I noticed it's like this from v7.
> 
Hi Marco,

Yes, that is correct. Thank you for bringing this to my attention.

Kind regards,
-- 
Aaron Tomlin

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

[PATCH v11 12/13] genirq/affinity: Restrict managed IRQ affinity to housekeeping CPUs

[Aaron Tomlin]

At present, the managed interrupt spreading algorithm distributes vectors
across all available CPUs within a given node or system. On systems
employing CPU isolation (e.g., "isolcpus=io_queue"), this behaviour
defeats the primary purpose of isolation by routing hardware interrupts
(such as NVMe completion queues) directly to isolated cores.

Update irq_create_affinity_masks() to respect the housekeeping CPU mask.
Introduce irq_spread_hk_filter() to intersect the natively calculated
affinity mask with the HK_TYPE_IO_QUEUE mask, thereby keeping managed
interrupts off isolated CPUs.

To ensure strict isolation whilst guaranteeing a valid routing destination:

    1.  Fallback mechanism: Should the initial spreading logic assign a
        vector exclusively to isolated CPUs (resulting in an empty
        intersection), the filter safely falls back to the system's
        online housekeeping CPUs.

    2.  Hotplug safety: The fallback utilises data_race(cpu_online_mask)
        instead of allocating a local cpumask snapshot. This circumvents
        CONFIG_CPUMASK_OFFSTACK stack bloat hazards on high-core-count
        systems. Furthermore, it prevents deadlocks with concurrent CPU
        hotplug operations (e.g., during storage driver error recovery)
        by eliminating the need to hold the CPU hotplug read lock.

    3.  Fast-path optimisation: The filtering logic is conditionally
        executed only if housekeeping is enabled, thereby ensuring zero
        overhead for standard configurations.

Signed-off-by: Aaron Tomlin <atomlin@atomlin.com>
---
 kernel/irq/affinity.c | 26 +++++++++++++++++++++++++-
 1 file changed, 25 insertions(+), 1 deletion(-)

diff --git a/kernel/irq/affinity.c b/kernel/irq/affinity.c
index e0cf70a99339..03e914ffd720 100644
--- a/kernel/irq/affinity.c
+++ b/kernel/irq/affinity.c
@@ -8,6 +8,24 @@
 #include <linux/slab.h>
 #include <linux/cpu.h>
 #include <linux/group_cpus.h>
+#include <linux/sched/isolation.h>
+
+/**
+ * irq_spread_hk_filter - Restrict an interrupt affinity mask to housekeeping CPUs
+ * @mask:            The interrupt affinity mask to filter (in/out)
+ * @hk_mask:         The system's housekeeping CPU mask
+ *
+ * Intersects @mask with @hk_mask to keep interrupts off isolated CPUs.
+ * If this intersection is empty (meaning all targeted CPUs were isolated),
+ * it falls back to the online housekeeping CPUs to guarantee a valid
+ * routing destination.
+ */
+static void irq_spread_hk_filter(struct cpumask *mask,
+				 const struct cpumask *hk_mask)
+{
+	if (!cpumask_and(mask, mask, hk_mask))
+		cpumask_and(mask, hk_mask, data_race(cpu_online_mask));
+}
 
 static void default_calc_sets(struct irq_affinity *affd, unsigned int affvecs)
 {
@@ -27,6 +45,8 @@ irq_create_affinity_masks(unsigned int nvecs, struct irq_affinity *affd)
 {
 	unsigned int affvecs, curvec, usedvecs, i;
 	struct irq_affinity_desc *masks = NULL;
+	const struct cpumask *hk_mask = housekeeping_cpumask(HK_TYPE_IO_QUEUE);
+	bool hk_enabled = housekeeping_enabled(HK_TYPE_IO_QUEUE);
 
 	/*
 	 * Determine the number of vectors which need interrupt affinities
@@ -83,8 +103,12 @@ irq_create_affinity_masks(unsigned int nvecs, struct irq_affinity *affd)
 			return NULL;
 		}
 
-		for (int j = 0; j < nr_masks; j++)
+		for (int j = 0; j < nr_masks; j++) {
 			cpumask_copy(&masks[curvec + j].mask, &result[j]);
+			if (hk_enabled)
+				irq_spread_hk_filter(&masks[curvec + j].mask,
+						     hk_mask);
+		}
 		kfree(result);
 
 		curvec += nr_masks;
-- 
2.51.0

[PATCH v11 13/13] docs: add io_queue flag to isolcpus

[Aaron Tomlin]

From: Daniel Wagner <wagi@kernel.org>

The io_queue flag informs multiqueue device drivers where to place
hardware queues. Document this new flag in the isolcpus
command-line argument description.

Signed-off-by: Daniel Wagner <wagi@kernel.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
[atomlin: Refined io_queue kernel parameter documentation]
Signed-off-by: Aaron Tomlin <atomlin@atomlin.com>
---
 .../admin-guide/kernel-parameters.txt         | 30 ++++++++++++++++++-
 1 file changed, 29 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 4510b4b3c416..52ede95db56f 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2827,7 +2827,6 @@ Kernel parameters
 			  "number of CPUs in system - 1".
 
 			managed_irq
-
 			  Isolate from being targeted by managed interrupts
 			  which have an interrupt mask containing isolated
 			  CPUs. The affinity of managed interrupts is
@@ -2850,6 +2849,35 @@ Kernel parameters
 			  housekeeping CPUs has no influence on those
 			  queues.
 
+			io_queue
+			  Applicable to managed IRQs only. Restrict
+			  multiqueue hardware queue allocation to online
+			  housekeeping CPUs. This guarantees that all
+			  managed hardware completion interrupts are routed
+			  exclusively to housekeeping cores, shielding
+			  isolated CPUs from I/O interruptions even if they
+			  initiated the request.
+
+			  The io_queue configuration takes precedence over
+			  managed_irq. When io_queue is used, managed_irq
+			  placement constraints have no effect.
+
+			  Note: Using io_queue restricts the number of
+			  allocated hardware queues to match the number of
+			  housekeeping CPUs. This prevents MSI-X vector
+			  exhaustion and forces isolated CPUs to share
+			  submission queues.
+
+			  Note: Offlining housekeeping CPUs which serve
+			  isolated CPUs will fail. The isolated CPUs must
+			  be offlined before offlining the housekeeping
+			  CPUs.
+
+			  Note: When I/O is submitted by an application on
+			  an isolated CPU, the hardware completion
+			  interrupt is handled entirely by a housekeeping
+			  CPU.
+
 			The format of <cpu-list> is described above.
 
 	iucv=		[HW,NET]
-- 
2.51.0

Re: [PATCH v11 00/13] blk: honor isolcpus configuration

[Aaron Tomlin]

On Thu, Apr 16, 2026 at 03:29:29PM -0400, Aaron Tomlin wrote:
> Please let me know your thoughts.

My apologies, I neglected to include the changelog.

Changes in v11:

 - Completely rewrote the isolcpus=io_queue documentation in
   Documentation/admin-guide/kernel-parameters.txt to clarify its exclusive
   application to managed IRQs, queue allocation limits, vector exhaustion
   prevention, and hardware interrupt routing (Ming Lei)

 - Fixed a stack frame bloat issue by avoiding the on-stack declaration of
   struct cpumask (Waiman Long)

 - Linked to v10: https://lore.kernel.org/linux-nvme/20260401222312.772334-1-atomlin@atomlin.com/

Changes in v10:

 - Fixed a page fault regression encountered when initialising secondary
   queue maps (e.g., NVMe poll queues). Restored the qmap->queue_offset to
   the mq_map assignment to ensure CPUs are strictly mapped to absolute
   hardware indices (Keith Busch)

 - Corrected the active_hctx tracker to utilise relative queue indices,
   preventing out-of-bounds mask assignments

 - Fixed the blk_mq_validate() sanity check to properly evaluate absolute
   queue indices against the offset-adjusted loop index

 - Corrected typographical errors within block/blk-mq-cpumap.c
   (Keith Busch)

 - Clarified the commit message regarding the removal of the !SMP fallback
   code, explicitly noting that the core scheduler now mandates SMP
   unconditionally (Sebastian Andrzej Siewior)

 - Added missing "Signed-off-by:" tags to properly record the patch series
   chain of custody

 - Linked to v9: https://lore.kernel.org/lkml/20260330221047.630206-1-atomlin@atomlin.com/

Changes in v9:

 - Added "Reviewed-by:" tags

 - Introduced irq_spread_hk_filter() to safely restrict managed IRQ
   affinity to housekeeping CPUs (Thomas Gleixner)

 - Removed the unsafe global static variable blk_hk_online_mask from
   blk-mq-cpumap.c and blk-mq.c. blk_mq_online_queue_affinity() now returns
   a stable pointer, delegating safe intersection to the callers to prevent
   concurrent modification races (Thomas Gleixner, Hannes Reinecke)

 - Resolved BUG: kernel NULL pointer dereference in __blk_mq_all_tag_iter
   reported by the kernel test robot during cpuhotplug rcutorture stress
   testing

 - Linked to v8: https://lore.kernel.org/lkml/20250905-isolcpus-io-queues-v8-0-885984c5daca@kernel.org/

Changes in v8:

 - Added commit 524f5eea4bbe ("lib/group_cpus: remove !SMP code")

 - Merged the new mapping logic directly into the existing function to
   avoid special casing

 - Refined the group_mask_cpus_evenly() implementation with the following
   updates:

   - Corrected the function name typo (changed group_masks_cpus_evenly to
     group_mask_cpus_evenly)

   - Updated the documentation comment to accurately reflect the function's
     behavior

   - Renamed the cpu_mask argument to mask for consistency

 - Added a new patch for aacraid to include the missing number of queues
   calculation

 - Restricted updates to only affect SCSI drivers that support
   PCI_IRQ_AFFINITY and do not utilize nvme-fabrics

 - Removed the __free cleanup attribute usage for cpumask_var_t allocations
   due to compatibility issues

 - Updated the documentation to explicitly highlight the limitations
   surrounding CPU offlining

 - Collected accumulated Reviewed-by and Acked-by tags

 - Linked to v7: https://patch.msgid.link/20250702-isolcpus-io-queues-v7-0-557aa7eacce4@kernel.org

Changes in v7:

 - Sent out the first part of the series independently:
   https://lore.kernel.org/all/20250617-isolcpus-queue-counters-v1-0-13923686b54b@kernel.org/

 - Added comprehensive kernel command-line documentation

 - Added validation logic to ensure the resulting CPU-to-queue mapping is
   fully operational

 - Rewrote the isolcpus mapping code to properly account for active
   hardware contexts (hctx)

 - Introduced blk_mq_map_hk_irq_queues, which utilizes the mask retrieved
   from irq_get_affinity()

 - Refactored blk_mq_map_hk_queues to require the caller to explicitly test
   for HK_TYPE_MANAGED_IRQ

 - Linked to v6: https://patch.msgid.link/20250424-isolcpus-io-queues-v6-0-9a53a870ca1f@kernel.org

Changes in v6:

 - Reintroduced the io_queue type for the isolcpus kernel parameter

 - Prevented the offlining of a housekeeping CPU if an isolated CPU is
   still present, upgrading this behavior from a simple warning to a hard
   restriction

 - Linked to v5: https://lore.kernel.org/r/20250110-isolcpus-io-queues-v5-0-0e4f118680b0@kernel.org

Changes in v5:

 - Rebased the series onto the latest for-6.14/block branch.

 - Updated the documentation regarding the managed_irq parameters

 - Reworded the commit message for "blk-mq: issue warning when offlining
   hctx with online isolcpus" for better clarity

 - Split the input and output parameters in the patch "lib/group_cpus: let
   group_cpu_evenly return number of groups"

 - Dropped the patch "sched/isolation: document HK_TYPE housekeeping
   option"

 - Linked to v4: https://lore.kernel.org/r/20241217-isolcpus-io-queues-v4-0-5d355fbb1e14@kernel.org

Changes in v4:

 - Added the patch "blk-mq: issue warning when offlining hctx with online
   isolcpus"

 - Fixed the check in group_cpus_evenly(); the condition now properly uses
   housekeeping_enabled() instead of cpumask_weight(), as the latter always
   returns a valid mask

 - Dropped the Fixes: tag from "lib/group_cpus.c: honor housekeeping config
   when grouping CPUs"

 - Fixed an overlong line warning in the patch "scsi: use block layer
   helpers to calculate num of queues"

 - Dropped the patch "sched/isolation: Add io_queue housekeeping option" in
   favor of simply documenting the housekeeping hk_type enum

 - Added the patch "lib/group_cpus: let group_cpu_evenly return number of
   groups"

 - Collected accumulated Reviewed-by and Acked-by tags

 - Split the patchset by moving foundational changes into a separate
   preparation series:
   https://lore.kernel.org/linux-nvme/20241202-refactor-blk-affinity-helpers-v6-0-27211e9c2cd5@kernel.org/

 - Linked to v3: https://lore.kernel.org/r/20240806-isolcpus-io-queues-v3-0-da0eecfeaf8b@suse.de

Changes in v3:

 - Integrated patches from Ming Lei
   (https://lore.kernel.org/all/20210709081005.421340-1-ming.lei@redhat.com/):
   "virtio: add APIs for retrieving vq affinity" and "blk-mq: introduce
   blk_mq_dev_map_queues"

 - Replaced all instances of blk_mq_pci_map_queues and
   blk_mq_virtio_map_queues with the new unified blk_mq_dev_map_queues

 - Updated and expanded the helper functions used for calculating the
   number of queues

 - Added the CPU-to-hctx mapping function specifically to support the
   isolcpus=io_queue parameter

 - Documented the hk_type enum and the newly introduced isolcpus=io_queue
   parameter

 - Added the patch "scsi: pm8001: do not overwrite PCI queue mapping"

 - Linked to v2: https://lore.kernel.org/r/20240627-isolcpus-io-queues-v2-0-26a32e3c4f75@suse.de

Changes in v2:

 - Updated the feature documentation for clarity and completeness

 - Split the blk/nvme-pci patch into smaller, logical commits

 - Dropped the HK_TYPE_IO_QUEUE macro in favor of reusing
   HK_TYPE_MANAGED_IRQ

 - Linked to v1: https://lore.kernel.org/r/20240621-isolcpus-io-queues-v1-0-8b169bf41083@suse.de

> 
> Aaron Tomlin (1):
>   genirq/affinity: Restrict managed IRQ affinity to housekeeping CPUs
> 
> Daniel Wagner (12):
>   scsi: aacraid: use block layer helpers to calculate num of queues
>   lib/group_cpus: remove dead !SMP code
>   lib/group_cpus: Add group_mask_cpus_evenly()
>   genirq/affinity: Add cpumask to struct irq_affinity
>   blk-mq: add blk_mq_{online|possible}_queue_affinity
>   nvme-pci: use block layer helpers to constrain queue affinity
>   scsi: Use block layer helpers to constrain queue affinity
>   virtio: blk/scsi: use block layer helpers to constrain queue affinity
>   isolation: Introduce io_queue isolcpus type
>   blk-mq: use hk cpus only when isolcpus=io_queue is enabled
>   blk-mq: prevent offlining hk CPUs with associated online isolated CPUs
>   docs: add io_queue flag to isolcpus
> 
>  .../admin-guide/kernel-parameters.txt         |  30 ++-
>  block/blk-mq-cpumap.c                         | 192 ++++++++++++++++--
>  block/blk-mq.c                                |  42 ++++
>  drivers/block/virtio_blk.c                    |   4 +-
>  drivers/nvme/host/pci.c                       |   1 +
>  drivers/scsi/aacraid/comminit.c               |   3 +-
>  drivers/scsi/hisi_sas/hisi_sas_v3_hw.c        |   1 +
>  drivers/scsi/megaraid/megaraid_sas_base.c     |   5 +-
>  drivers/scsi/mpi3mr/mpi3mr_fw.c               |   6 +-
>  drivers/scsi/mpt3sas/mpt3sas_base.c           |   5 +-
>  drivers/scsi/pm8001/pm8001_init.c             |   1 +
>  drivers/scsi/virtio_scsi.c                    |   5 +-
>  include/linux/blk-mq.h                        |   2 +
>  include/linux/group_cpus.h                    |   3 +
>  include/linux/interrupt.h                     |  16 +-
>  include/linux/sched/isolation.h               |   1 +
>  kernel/irq/affinity.c                         |  38 +++-
>  kernel/sched/isolation.c                      |   7 +
>  lib/group_cpus.c                              |  65 ++++--
>  19 files changed, 379 insertions(+), 48 deletions(-)
> 
> 
> base-commit: 3cd8b194bf3428dfa53120fee47e827a7c495815
> -- 
> 2.51.0
> 

-- 
Aaron Tomlin