Re: [PATCH v4 05/23] iommufd/driver: Let iommufd_viommu_alloc helper save ictx to viommu->ictx

Nicolin Chen
2025-05-27T18:41:48Z

On Mon, May 26, 2025 at 10:30:46AM -0300, Jason Gunthorpe wrote:
> On Fri, May 16, 2025 at 01:56:26PM -0700, Nicolin Chen wrote:
>
> > > You don't need to move this unless you are using inlines. Just use a
> > > forward declaration.
> >
> > Since we forward ucmd now, ictx is in the ucmd so we need this
> > structure for:
> >
> > - if (!IS_ERR(ret)) \
> > + if (!IS_ERR(ret)) { \
> > ret->member.ops = viommu_ops; \
> > + ret->member.ictx = ucmd->ictx; \
> > + } \
>
> De-inline more of that function probably..
>
> Also seem my other remarks about not storing ictx so much..

I found that all other ictx pointers in vdev/hw_queue are unused,
as the core simply gets an ictx from their viommu pointers. This
means that only this viommu allocator here needs such a storing.

With that, how about a change like this v.s. inline:

[ Sol-1: Store ucmd ]
----------------------------------------------------------------------------
diff --git a/drivers/iommu/iommufd/viommu.c b/drivers/iommu/iommufd/viommu.c
index 2b30627d1d8ed..513af9ba04f17 100644
--- a/drivers/iommu/iommufd/viommu.c
+++ b/drivers/iommu/iommufd/viommu.c
@@ -60,9 +60,15 @@ int iommufd_viommu_alloc_ioctl(struct iommufd_ucmd *ucmd)
goto out_put_hwpt;
}

+ /* Verify if the driver correctly calls iommufd_viommu_alloc() */
+ static_assert(offsetof(typeof(*ucmd), ictx) == 0);
+ if (WARN_ON_ONCE(viommu->ictx != ucmd->ictx)) {
+ rc = -EINVAL;
+ goto out_put_hwpt;
+ }
+
xa_init(&viommu->vdevs);
viommu->type = cmd->type;
- viommu->ictx = ucmd->ictx;
viommu->hwpt = hwpt_paging;
refcount_inc(&viommu->hwpt->common.obj.users);
INIT_LIST_HEAD(&viommu->veventqs);
diff --git a/include/linux/iommufd.h b/include/linux/iommufd.h
index d74c97feb9b52..6843c748a6f74 100644
--- a/include/linux/iommufd.h
+++ b/include/linux/iommufd.h
@@ -104,7 +104,10 @@ void iommufd_ctx_get(struct iommufd_ctx *ictx);

struct iommufd_viommu {
struct iommufd_object obj;
- struct iommufd_ctx *ictx;
+ union {
+ struct iommufd_ctx *ictx;
+ struct iommufd_ucmd *ucmd; /* for allocation only */
+ };
struct iommu_device *iommu_dev;
struct iommufd_hwpt_paging *hwpt;

@@ -262,8 +265,10 @@ static inline int iommufd_viommu_report_event(struct iommufd_viommu *viommu,
\
ret = (drv_struct *)__iommufd_object_alloc_ucmd( \
ucmd, ret, IOMMUFD_OBJ_VIOMMU, member.obj); \
- if (!IS_ERR(ret)) \
+ if (!IS_ERR(ret)) { \
ret->member.ops = viommu_ops; \
+ ret->member.ucmd = ucmd; \
+ } \
ret; \
})
#endif
----------------------------------------------------------------------------

[ Sol-2: De-inline ]
----------------------------------------------------------------------------
diff --git a/drivers/iommu/iommufd/driver.c b/drivers/iommu/iommufd/driver.c
index 28dec9e097204..0adb1a552e457 100644
--- a/drivers/iommu/iommufd/driver.c
+++ b/drivers/iommu/iommufd/driver.c
@@ -54,6 +54,23 @@ struct iommufd_object *_iommufd_object_alloc_ucmd(struct iommufd_ucmd *ucmd,
}
EXPORT_SYMBOL_NS_GPL(_iommufd_object_alloc_ucmd, "IOMMUFD");

+struct iommufd_viommu *
+_iommufd_viommu_alloc_ucmd(struct iommufd_ucmd *ucmd, size_t size,
+ const struct iommufd_viommu_ops *viommu_ops)
+{
+ struct iommufd_viommu *viommu;
+
+ static_assert(offsetof(typeof(*viommu), obj) == 0);
+ viommu = (struct iommufd_viommu *)_iommufd_object_alloc_ucmd(
+ ucmd, size, IOMMUFD_OBJ_VIOMMU);
+ if (IS_ERR(viommu))
+ return viommu;
+ viommu->ops = viommu_ops;
+ viommu->ictx = ucmd->ictx;
+ return viommu;
+}
+EXPORT_SYMBOL_NS_GPL(_iommufd_viommu_alloc_ucmd, "IOMMUFD");
+
/* Caller should xa_lock(&viommu->vdevs) to protect the return value */
struct device *iommufd_viommu_find_dev(struct iommufd_viommu *viommu,
unsigned long vdev_id)
diff --git a/drivers/iommu/iommufd/viommu.c b/drivers/iommu/iommufd/viommu.c
index 2b30627d1d8ed..259fcfd85b1bd 100644
--- a/drivers/iommu/iommufd/viommu.c
+++ b/drivers/iommu/iommufd/viommu.c
@@ -60,9 +60,14 @@ int iommufd_viommu_alloc_ioctl(struct iommufd_ucmd *ucmd)
goto out_put_hwpt;
}

+ /* Verify if the driver correctly calls iommufd_viommu_alloc() */
+ if (WARN_ON_ONCE(viommu->ictx != ucmd->ictx)) {
+ rc = -EINVAL;
+ goto out_put_hwpt;
+ }
+
xa_init(&viommu->vdevs);
viommu->type = cmd->type;
- viommu->ictx = ucmd->ictx;
viommu->hwpt = hwpt_paging;
refcount_inc(&viommu->hwpt->common.obj.users);
INIT_LIST_HEAD(&viommu->veventqs);
diff --git a/include/linux/iommufd.h b/include/linux/iommufd.h
index d74c97feb9b52..50ac3a5703520 100644
--- a/include/linux/iommufd.h
+++ b/include/linux/iommufd.h
@@ -209,6 +209,9 @@ struct iommufd_object *_iommufd_object_alloc(struct iommufd_ctx *ictx,
struct iommufd_object *
_iommufd_object_alloc_ucmd(struct iommufd_ucmd *ucmd, size_t size,
enum iommufd_object_type type);
+struct iommufd_viommu *
+_iommufd_viommu_alloc_ucmd(struct iommufd_ucmd *ucmd, size_t size,
+ const struct iommufd_viommu_ops *viommu_ops);
struct device *iommufd_viommu_find_dev(struct iommufd_viommu *viommu,
unsigned long vdev_id);
int iommufd_viommu_get_vdev_id(struct iommufd_viommu *viommu,
@@ -231,6 +234,13 @@ _iommufd_object_alloc_ucmd(struct iommufd_ucmd *ucmd, size_t size,
return ERR_PTR(-EOPNOTSUPP);
}

+static inline struct iommufd_viommu *
+_iommufd_viommu_alloc_ucmd(struct iommufd_ucmd *ucmd, size_t size,
+ const struct iommufd_viommu_ops *viommu_ops)
+{
+ return ERR_PTR(-EOPNOTSUPP);
+}
+
static inline struct device *
iommufd_viommu_find_dev(struct iommufd_viommu *viommu, unsigned long vdev_id)
{
@@ -257,13 +267,7 @@ static inline int iommufd_viommu_report_event(struct iommufd_viommu *viommu,
* the iommufd core. The free op will be called prior to freeing the memory.
*/
#define iommufd_viommu_alloc(ucmd, drv_struct, member, viommu_ops) \
- ({ \
- drv_struct *ret; \
- \
- ret = (drv_struct *)__iommufd_object_alloc_ucmd( \
- ucmd, ret, IOMMUFD_OBJ_VIOMMU, member.obj); \
- if (!IS_ERR(ret)) \
- ret->member.ops = viommu_ops; \
- ret; \
- })
+ container_of(_iommufd_viommu_alloc_ucmd( \
+ ucmd, sizeof(drv_struct), viommu_ops), \
+ typeof(drv_struct), member)
#endif
----------------------------------------------------------------------------

Thanks
Nicolin