[PATCH v9 4/7] iommu/arm-smmu-v3: Pre-allocate a per-master invalidation array

Nicolin Chen
2025-12-19T20:12:36Z

When a master is attached from an old domain to a new domain, it needs to
build an invalidation array to delete and add the array entries from/onto
the invalidation arrays of those two domains, passed via the to_merge and
to_unref arguments into arm_smmu_invs_merge/unref() respectively.

Since the master->num_streams might differ across masters, a memory would
have to be allocated when building an to_merge/to_unref array which might
fail with -ENOMEM.

On the other hand, an attachment to arm_smmu_blocked_domain must not fail
so it's the best to avoid any memory allocation in that path.

Pre-allocate a fixed size invalidation array for every master. This array
will be used as a scratch to fill dynamically when building a to_merge or
to_unref invs array. Sort fwspec->ids in an ascending order to fit to the
arm_smmu_invs_merge() function.

Co-developed-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
---
drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h | 8 ++++
drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 41 +++++++++++++++++++--
2 files changed, 45 insertions(+), 4 deletions(-)

diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
index a9441dc9070e..f98774962012 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
@@ -930,6 +930,14 @@ struct arm_smmu_master {
struct arm_smmu_device *smmu;
struct device *dev;
struct arm_smmu_stream *streams;
+ /*
+ * Scratch memory for a to_merge or to_unref array to build a per-domain
+ * invalidation array. It'll be pre-allocated with enough enries for all
+ * possible build scenarios. It can be used by only one caller at a time
+ * until the arm_smmu_invs_merge/unref() finishes. Must be locked by the
+ * iommu_group mutex.
+ */
+ struct arm_smmu_invs *build_invs;
struct arm_smmu_vmaster *vmaster; /* use smmu->streams_mutex */
/* Locked by the iommu core using the group mutex */
struct arm_smmu_ctx_desc_cfg cd_table;
diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
index 39e89176fa87..cc85e7a10ea8 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
@@ -3709,12 +3709,22 @@ static int arm_smmu_init_sid_strtab(struct arm_smmu_device *smmu, u32 sid)
return 0;
}

+static int arm_smmu_stream_id_cmp(const void *_l, const void *_r)
+{
+ const typeof_member(struct arm_smmu_stream, id) *l = _l;
+ const typeof_member(struct arm_smmu_stream, id) *r = _r;
+
+ return cmp_int(*l, *r);
+}
+
static int arm_smmu_insert_master(struct arm_smmu_device *smmu,
struct arm_smmu_master *master)
{
int i;
int ret = 0;
struct iommu_fwspec *fwspec = dev_iommu_fwspec_get(master->dev);
+ bool ats_supported = dev_is_pci(master->dev) &&
+ pci_ats_supported(to_pci_dev(master->dev));

master->streams = kcalloc(fwspec->num_ids, sizeof(*master->streams),
GFP_KERNEL);
@@ -3722,14 +3732,35 @@ static int arm_smmu_insert_master(struct arm_smmu_device *smmu,
return -ENOMEM;
master->num_streams = fwspec->num_ids;

- mutex_lock(&smmu->streams_mutex);
+ if (!ats_supported) {
+ /* Base case has 1 ASID entry or maximum 2 VMID entries */
+ master->build_invs = arm_smmu_invs_alloc(2);
+ } else {
+ /* ATS case adds num_ids of entries, on top of the base case */
+ master->build_invs = arm_smmu_invs_alloc(2 + fwspec->num_ids);
+ }
+ if (!master->build_invs) {
+ kfree(master->streams);
+ return -ENOMEM;
+ }
+
for (i = 0; i < fwspec->num_ids; i++) {
struct arm_smmu_stream *new_stream = &master->streams[i];
- struct rb_node *existing;
- u32 sid = fwspec->ids[i];

- new_stream->id = sid;
+ new_stream->id = fwspec->ids[i];
new_stream->master = master;
+ }
+
+ /* Put the ids into order for sorted to_merge/to_unref arrays */
+ sort_nonatomic(master->streams, master->num_streams,
+ sizeof(master->streams[0]), arm_smmu_stream_id_cmp,
+ NULL);
+
+ mutex_lock(&smmu->streams_mutex);
+ for (i = 0; i < fwspec->num_ids; i++) {
+ struct arm_smmu_stream *new_stream = &master->streams[i];
+ struct rb_node *existing;
+ u32 sid = new_stream->id;

ret = arm_smmu_init_sid_strtab(smmu, sid);
if (ret)
@@ -3759,6 +3790,7 @@ static int arm_smmu_insert_master(struct arm_smmu_device *smmu,
for (i--; i >= 0; i--)
rb_erase(&master->streams[i].node, &smmu->streams);
kfree(master->streams);
+ kfree(master->build_invs);
}
mutex_unlock(&smmu->streams_mutex);

@@ -3780,6 +3812,7 @@ static void arm_smmu_remove_master(struct arm_smmu_master *master)
mutex_unlock(&smmu->streams_mutex);

kfree(master->streams);
+ kfree(master->build_invs);
}

static struct iommu_device *arm_smmu_probe_device(struct device *dev)
--
2.43.0