linux-kernel - [PATCH v2 13/14] iommufd: Introduce iommufd_object_alloc

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Message-ID: <e7206d4227844887cc8dbf0cc7b0242580fafd9d.1749882255.git.nicolinc@nvidia.com>
Date: Fri, 13 Jun 2025 23:35:25 -0700
From: Nicolin Chen <nicolinc@...dia.com>
To: <jgg@...dia.com>, <kevin.tian@...el.com>
CC: <will@...nel.org>, <robin.murphy@....com>, <joro@...tes.org>,
	<praan@...gle.com>, <yi.l.liu@...el.com>, <peterz@...radead.org>,
	<jsnitsel@...hat.com>, <linux-arm-kernel@...ts.infradead.org>,
	<iommu@...ts.linux.dev>, <linux-kernel@...r.kernel.org>,
	<patches@...ts.linux.dev>, <baolu.lu@...ux.intel.com>
Subject: [PATCH v2 13/14] iommufd: Introduce iommufd_object_alloc_ucmd helper

An object allocator needs to call either iommufd_object_finalize() upon a
success or iommufd_object_abort_and_destroy() upon an error code.

To reduce duplication, store a new_obj in the struct iommufd_ucmd and call
iommufd_object_finalize/iommufd_object_abort_and_destroy() accordingly in
the main function.

Similar to iommufd_object_alloc() and __iommufd_object_alloc(), add a pair
of helpers: __iommufd_object_alloc_ucmd() and iommufd_object_alloc_ucmd().

Suggested-by: Jason Gunthorpe <jgg@...dia.com>
Reviewed-by: Kevin Tian <kevin.tian@...el.com>
Reviewed-by: Jason Gunthorpe <jgg@...dia.com>
Signed-off-by: Nicolin Chen <nicolinc@...dia.com>
---
 drivers/iommu/iommufd/iommufd_private.h | 26 +++++++++++++++++++++++++
 drivers/iommu/iommufd/main.c            | 25 ++++++++++++++++++++++++
 2 files changed, 51 insertions(+)

diff --git a/drivers/iommu/iommufd/iommufd_private.h b/drivers/iommu/iommufd/iommufd_private.h
index ec5b499d139c..4f5e8cd99c96 100644
--- a/drivers/iommu/iommufd/iommufd_private.h
+++ b/drivers/iommu/iommufd/iommufd_private.h
@@ -135,6 +135,7 @@ struct iommufd_ucmd {
 	void __user *ubuffer;
 	u32 user_size;
 	void *cmd;
+	struct iommufd_object *new_obj;
 };
 
 int iommufd_vfio_ioctl(struct iommufd_ctx *ictx, unsigned int cmd,
@@ -230,6 +231,11 @@ iommufd_object_put_and_try_destroy(struct iommufd_ctx *ictx,
 	iommufd_object_remove(ictx, obj, obj->id, 0);
 }
 
+/*
+ * Callers of these normal object allocators must call iommufd_object_finalize()
+ * to finalize the object, or call iommufd_object_abort_and_destroy() to revert
+ * the allocation.
+ */
 struct iommufd_object *_iommufd_object_alloc(struct iommufd_ctx *ictx,
 					     size_t size,
 					     enum iommufd_object_type type);
@@ -246,6 +252,26 @@ struct iommufd_object *_iommufd_object_alloc(struct iommufd_ctx *ictx,
 #define iommufd_object_alloc(ictx, ptr, type) \
 	__iommufd_object_alloc(ictx, ptr, type, obj)
 
+/*
+ * Callers of these _ucmd allocators should not call iommufd_object_finalize()
+ * or iommufd_object_abort_and_destroy(), as the core automatically does that.
+ */
+struct iommufd_object *
+_iommufd_object_alloc_ucmd(struct iommufd_ucmd *ucmd, size_t size,
+			   enum iommufd_object_type type);
+
+#define __iommufd_object_alloc_ucmd(ucmd, ptr, type, obj)                      \
+	container_of(_iommufd_object_alloc_ucmd(                               \
+			     ucmd,                                             \
+			     sizeof(*(ptr)) + BUILD_BUG_ON_ZERO(               \
+						      offsetof(typeof(*(ptr)), \
+							       obj) != 0),     \
+			     type),                                            \
+		     typeof(*(ptr)), obj)
+
+#define iommufd_object_alloc_ucmd(ucmd, ptr, type) \
+	__iommufd_object_alloc_ucmd(ucmd, ptr, type, obj)
+
 /*
  * The IO Address Space (IOAS) pagetable is a virtual page table backed by the
  * io_pagetable object. It is a user controlled mapping of IOVA -> PFNs. The
diff --git a/drivers/iommu/iommufd/main.c b/drivers/iommu/iommufd/main.c
index 85ad2853da0b..778694d7c207 100644
--- a/drivers/iommu/iommufd/main.c
+++ b/drivers/iommu/iommufd/main.c
@@ -61,6 +61,24 @@ struct iommufd_object *_iommufd_object_alloc(struct iommufd_ctx *ictx,
 	return ERR_PTR(rc);
 }
 
+struct iommufd_object *_iommufd_object_alloc_ucmd(struct iommufd_ucmd *ucmd,
+						  size_t size,
+						  enum iommufd_object_type type)
+{
+	struct iommufd_object *new_obj;
+
+	/* Something is coded wrong if this is hit */
+	if (WARN_ON(ucmd->new_obj))
+		return ERR_PTR(-EBUSY);
+
+	new_obj = _iommufd_object_alloc(ucmd->ictx, size, type);
+	if (IS_ERR(new_obj))
+		return new_obj;
+
+	ucmd->new_obj = new_obj;
+	return new_obj;
+}
+
 /*
  * Allow concurrent access to the object.
  *
@@ -448,6 +466,13 @@ static long iommufd_fops_ioctl(struct file *filp, unsigned int cmd,
 	if (ret)
 		return ret;
 	ret = op->execute(&ucmd);
+
+	if (ucmd.new_obj) {
+		if (ret)
+			iommufd_object_abort_and_destroy(ictx, ucmd.new_obj);
+		else
+			iommufd_object_finalize(ictx, ucmd.new_obj);
+	}
 	return ret;
 }
 
-- 
2.43.0