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

[Jason Gunthorpe <jgg@xxxxxxxxxx>]

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.

Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
---
 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 c9a05bb49bfa17..d5e86985f6d363 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -2948,8 +2948,7 @@ 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;
 
@@ -2982,13 +2981,18 @@ 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 ddc25d2391063b..66ea1d08dc3f58 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -668,7 +668,8 @@ 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