Re: [PATCH v12 5/5] iommu/vt-d: improve ITE fault handling if target device isn't present

Jason Gunthorpe
2024-02-01T19:34:29Z

On Wed, Jan 31, 2024 at 02:21:20PM +0800, Baolu Lu wrote:
> An rbtree for IOMMU device data for the VT-d driver would be beneficial.
> It also benefits other paths of fault handling, such as the I/O page
> fault handling path, where it currently still relies on the PCI
> subsystem to convert a RID value into a pci_device structure.
>
> Given that such an rbtree would be helpful for multiple individual
> drivers that handle PCI devices, it seems valuable to implement it in
> the core?

rbtree is already supposed to be a re-usable library.

There is already good helper support in rbtree to make things easy to
implement. I see arm hasn't used them yet, it should look something
like this:

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 f58e77b99d476b..ebf86c6a8787c4 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
@@ -1673,26 +1673,37 @@ static int arm_smmu_init_l2_strtab(struct arm_smmu_device *smmu, u32 sid)
return 0;
}

+static int arm_smmu_streams_cmp_key(const void *lhs, const struct rb_node *rhs)
+{
+ struct arm_smmu_stream *stream_rhs =
+ rb_entry(rhs, struct arm_smmu_stream, node);
+ const u32 *sid_lhs = lhs;
+
+ if (*sid_lhs < stream_rhs->id)
+ return -1;
+ if (*sid_lhs > stream_rhs->id)
+ return 1;
+ return 0;
+}
+
+static int arm_smmu_streams_cmp_node(struct rb_node *lhs,
+ const struct rb_node *rhs)
+{
+ return arm_smmu_streams_cmp_key(
+ &rb_entry(lhs, struct arm_smmu_stream, node)->id, rhs);
+}
+
static struct arm_smmu_master *
arm_smmu_find_master(struct arm_smmu_device *smmu, u32 sid)
{
struct rb_node *node;
- struct arm_smmu_stream *stream;

lockdep_assert_held(&smmu->streams_mutex);

- node = smmu->streams.rb_node;
- while (node) {
- stream = rb_entry(node, struct arm_smmu_stream, node);
- if (stream->id < sid)
- node = node->rb_right;
- else if (stream->id > sid)
- node = node->rb_left;
- else
- return stream->master;
- }
-
- return NULL;
+ node = rb_find(&sid, &smmu->streams, arm_smmu_streams_cmp_key);
+ if (!node)
+ return NULL;
+ return rb_entry(node, struct arm_smmu_stream, node)->master;
}

/* IRQ and event handlers */
@@ -3324,8 +3335,6 @@ static int arm_smmu_insert_master(struct arm_smmu_device *smmu,
{
int i;
int ret = 0;
- struct arm_smmu_stream *new_stream, *cur_stream;
- struct rb_node **new_node, *parent_node = NULL;
struct iommu_fwspec *fwspec = dev_iommu_fwspec_get(master->dev);

master->streams = kcalloc(fwspec->num_ids, sizeof(*master->streams),
@@ -3336,6 +3345,7 @@ static int arm_smmu_insert_master(struct arm_smmu_device *smmu,

mutex_lock(&smmu->streams_mutex);
for (i = 0; i < fwspec->num_ids; i++) {
+ struct arm_smmu_stream *new_stream;
u32 sid = fwspec->ids[i];

new_stream = &master->streams[i];
@@ -3347,28 +3357,13 @@ static int arm_smmu_insert_master(struct arm_smmu_device *smmu,
break;

/* Insert into SID tree */
- new_node = &(smmu->streams.rb_node);
- while (*new_node) {
- cur_stream = rb_entry(*new_node, struct arm_smmu_stream,
- node);
- parent_node = *new_node;
- if (cur_stream->id > new_stream->id) {
- new_node = &((*new_node)->rb_left);
- } else if (cur_stream->id < new_stream->id) {
- new_node = &((*new_node)->rb_right);
- } else {
- dev_warn(master->dev,
- "stream %u already in tree\n",
- cur_stream->id);
- ret = -EINVAL;
- break;
- }
- }
- if (ret)
+ if (rb_find_add(&new_stream->node, &smmu->streams,
+ arm_smmu_streams_cmp_node)) {
+ dev_warn(master->dev, "stream %u already in tree\n",
+ sid);
+ ret = -EINVAL;
break;
-
- rb_link_node(&new_stream->node, parent_node, new_node);
- rb_insert_color(&new_stream->node, &smmu->streams);
+ }
}

if (ret) {