Re: [PATCH v4 06/23] iommufd/driver: Add iommufd_struct_destroy to revert iommufd_viommu_alloc

Jason Gunthorpe
2025-05-14T18:26:05Z

On Thu, May 08, 2025 at 08:02:27PM -0700, Nicolin Chen wrote:
> An IOMMU driver that allocated a vIOMMU may want to revert the allocation,
> if it encounters an internal error after the allocation. So, there needs a
> destroy helper for drivers to use. For instance:
>
> static my_viommu_alloc()
> {
> ...
> my_viommu = iommufd_viommu_alloc(viomm, struct my_viommu, core);
> ...
> ret = init_my_viommu();
> if (ret) {
> /* Need to destroy the my_viommu->core */
> return ERR_PTR(ret);
> }
> return &my_viommu->core;
> }
>
> Move iommufd_object_abort() to the driver.c file and the public header, to
> introduce common iommufd_struct_destroy() helper that will abort all kinds
> of driver structures, not confined to iommufd_viommu but also the new ones
> being added in the future.
>
> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
> Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
> Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
> ---
> drivers/iommu/iommufd/iommufd_private.h | 1 -
> include/linux/iommufd.h | 16 ++++++++++++++++
> drivers/iommu/iommufd/driver.c | 14 ++++++++++++++
> drivers/iommu/iommufd/main.c | 13 -------------
> 4 files changed, 30 insertions(+), 14 deletions(-)

One idea that struck me when I was looking at this was to copy the
technique from rdma.

When an object is allocated we keep track of it in the struct
iommufd_ucmd.

Then when the command is over the core code either aborts or finalizes
the objects in the iommufd_ucmd. This way you don't have to expose
abort and related to drivers.

Something like this:

diff --git a/drivers/iommu/iommufd/driver.c b/drivers/iommu/iommufd/driver.c
index 2d2695e2562d02..289dd19eec90f1 100644
--- a/drivers/iommu/iommufd/driver.c
+++ b/drivers/iommu/iommufd/driver.c
@@ -36,6 +36,16 @@ struct iommufd_object *_iommufd_object_alloc(struct iommufd_ctx *ictx,
}
EXPORT_SYMBOL_NS_GPL(_iommufd_object_alloc, "IOMMUFD");

+struct iommufd_object *_iommufd_object_alloc_ucmd(struct iommufd_ucmd *ucmd,
+ size_t size,
+ enum iommufd_object_type type)
+{
+ if (ucmd->alloced_obj)
+ return ERR_PTR(-EBUSY);
+ ucmd->alloced_obj = _iommufd_object_alloc(ucmd->ictx, size, type);
+ return ucmd->alloced_obj;
+}
+
/* Undo _iommufd_object_alloc() if iommufd_object_finalize() was not called */
void iommufd_object_abort(struct iommufd_ctx *ictx, struct iommufd_object *obj)
{
diff --git a/drivers/iommu/iommufd/eventq.c b/drivers/iommu/iommufd/eventq.c
index f39cf079734769..f109948a81ac8c 100644
--- a/drivers/iommu/iommufd/eventq.c
+++ b/drivers/iommu/iommufd/eventq.c
@@ -473,7 +473,7 @@ int iommufd_fault_alloc(struct iommufd_ucmd *ucmd)
if (cmd->flags)
return -EOPNOTSUPP;

- fault = __iommufd_object_alloc(ucmd->ictx, fault, IOMMUFD_OBJ_FAULT,
+ fault = __iommufd_object_alloc_ucmd(ucmd, fault, IOMMUFD_OBJ_FAULT,
common.obj);
if (IS_ERR(fault))
return PTR_ERR(fault);
@@ -483,10 +483,8 @@ int iommufd_fault_alloc(struct iommufd_ucmd *ucmd)

fdno = iommufd_eventq_init(&fault->common, "[iommufd-pgfault]",
ucmd->ictx, &iommufd_fault_fops);
- if (fdno < 0) {
- rc = fdno;
- goto out_abort;
- }
+ if (fdno < 0)
+ return fdno;

cmd->out_fault_id = fault->common.obj.id;
cmd->out_fault_fd = fdno;
@@ -494,7 +492,6 @@ int iommufd_fault_alloc(struct iommufd_ucmd *ucmd)
rc = iommufd_ucmd_respond(ucmd, sizeof(*cmd));
if (rc)
goto out_put_fdno;
- iommufd_object_finalize(ucmd->ictx, &fault->common.obj);

fd_install(fdno, fault->common.filep);

@@ -502,9 +499,6 @@ int iommufd_fault_alloc(struct iommufd_ucmd *ucmd)
out_put_fdno:
put_unused_fd(fdno);
fput(fault->common.filep);
-out_abort:
- iommufd_object_abort_and_destroy(ucmd->ictx, &fault->common.obj);
-
return rc;
}

diff --git a/drivers/iommu/iommufd/iommufd_private.h b/drivers/iommu/iommufd/iommufd_private.h
index c87326d7ecfccb..94cafae86d271c 100644
--- a/drivers/iommu/iommufd/iommufd_private.h
+++ b/drivers/iommu/iommufd/iommufd_private.h
@@ -152,6 +152,7 @@ struct iommufd_ucmd {
void __user *ubuffer;
u32 user_size;
void *cmd;
+ struct iommufd_object *alloced_obj;
};

int iommufd_vfio_ioctl(struct iommufd_ctx *ictx, unsigned int cmd,
@@ -258,6 +259,15 @@ iommufd_object_put_and_try_destroy(struct iommufd_ctx *ictx,
#define iommufd_object_alloc(ictx, ptr, type) \
__iommufd_object_alloc(ictx, ptr, type, obj)

+#define __iommufd_object_alloc_uctx(uctx, ptr, type, obj) \
+ container_of(_iommufd_object_alloc_ucmd( \
+ uctx, \
+ sizeof(*(ptr)) + BUILD_BUG_ON_ZERO( \
+ offsetof(typeof(*(ptr)), \
+ obj) != 0), \
+ type), \
+ typeof(*(ptr)), 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 1d7f3584aea0f7..0bc9c02f6bfc4f 100644
--- a/drivers/iommu/iommufd/main.c
+++ b/drivers/iommu/iommufd/main.c
@@ -408,6 +408,14 @@ static long iommufd_fops_ioctl(struct file *filp, unsigned int cmd,
if (ret)
return ret;
ret = op->execute(&ucmd);
+
+ if (ucmd.alloced_obj) {
+ if (ret)
+ iommufd_object_abort_and_destroy(ictx,
+ ucmd.alloced_obj);
+ else
+ iommufd_object_finalize(ictx, ucmd.alloced_obj);
+ }
return ret;
}