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

[Jason Gunthorpe <jgg@nvidia.com>]

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