[PATCH v2 05/17] iommu: Make iommu_fwspec->ids a distinct allocation

Jason Gunthorpe
2023-11-15T14:06:23Z

The optimization of kreallocing the entire fwspec only works if the fwspec
pointer is always stored in the dev->iommu. Since we want to change this
remove the optimization and make the ids array a distinct allocation.

Allow a single id to be stored inside the iommu_fwspec as a common case
optimization.

Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
---
drivers/iommu/iommu.c | 20 ++++++++++++--------
include/linux/iommu.h | 3 ++-
2 files changed, 14 insertions(+), 9 deletions(-)

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index f17a1113f3d6a3..18a82a20934d53 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -2931,8 +2931,7 @@ int iommu_fwspec_init(struct device *dev, struct fwnode_handle *iommu_fwnode,
if (!dev_iommu_get(dev))
return -ENOMEM;

- /* Preallocate for the overwhelmingly common case of 1 ID */
- fwspec = kzalloc(struct_size(fwspec, ids, 1), GFP_KERNEL);
+ fwspec = kzalloc(sizeof(*fwspec), GFP_KERNEL);
if (!fwspec)
return -ENOMEM;

@@ -2965,13 +2964,18 @@ int iommu_fwspec_add_ids(struct device *dev, u32 *ids, int num_ids)
return -EINVAL;

new_num = fwspec->num_ids + num_ids;
- if (new_num > 1) {
- fwspec = krealloc(fwspec, struct_size(fwspec, ids, new_num),
- GFP_KERNEL);
- if (!fwspec)
+ if (new_num <= 1) {
+ if (fwspec->ids != &fwspec->single_id)
+ kfree(fwspec->ids);
+ fwspec->ids = &fwspec->single_id;
+ } else if (new_num > fwspec->num_ids) {
+ ids = krealloc_array(
+ fwspec->ids != &fwspec->single_id ? fwspec->ids : NULL,
+ new_num, sizeof(fwspec->ids[0]),
+ GFP_KERNEL | __GFP_ZERO);
+ if (!ids)
return -ENOMEM;
-
- dev_iommu_fwspec_set(dev, fwspec);
+ fwspec->ids = ids;
}

for (i = 0; i < num_ids; i++)
diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index ec289c1016f5f2..e98a4ca8f536b7 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -798,7 +798,8 @@ struct iommu_fwspec {
struct fwnode_handle *iommu_fwnode;
u32 flags;
unsigned int num_ids;
- u32 ids[];
+ u32 single_id;
+ u32 *ids;
};

/* ATS is supported */
--
2.42.0