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

[Nicolin Chen]

On Fri, May 16, 2025 at 10:28:45AM -0300, Jason Gunthorpe wrote:
> On Thu, May 15, 2025 at 07:05:45PM -0700, Nicolin Chen wrote:
> 
> > Otherwise, they would be something like:
> >     // in my_viommu_alloc()
> >     my_viommu = iommufd_viommu_alloc(ucmd, ...);
> >     iommufd_viommu_alloc_mmap(ucmd->ictx, my_viommu, ...);
> >     iommufd_viommu_destroy_mmap(ucmd->ictx, my_viommu, ...);
> >     // in my_viommu_destory()
> >     iommufd_viommu_destroy_mmap(my_viommu->ictx, my_viommu ...);
> 
> Yes, this is how the other objects work..
> 
> > That being said, I ended up doing something more in this patch
> > for the ucmd rework and Kevin's comments:
> > 
> > diff --git a/drivers/iommu/iommufd/iommufd_private.h 
> > b/drivers/iommu/iommufd/iommufd_private.h
> > index 98fe5a49c9606..ddd144031af5d 100644
> > --- a/drivers/iommu/iommufd/iommufd_private.h
> > +++ b/drivers/iommu/iommufd/iommufd_private.h
> > @@ -136,14 +136,6 @@ int iopt_pin_pages(struct io_pagetable *iopt, unsigned 
> > long iova,
> >  void iopt_unpin_pages(struct io_pagetable *iopt, unsigned long iova,
> >                   unsigned long length);
> >  
> > -struct iommufd_ucmd {
> > -   struct iommufd_ctx *ictx;
> > -   void __user *ubuffer;
> > -   u32 user_size;
> > -   void *cmd;
> > -   struct iommufd_object *alloced_obj;
> > -};
> 
> 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;                         \
+               }                                                              \

Or, we could have a smaller:

#define ucmd_to_ictx(ucmd) (struct iommufd_ctx *)(ucmd)

and add a line of comments in struct iommufd_ucmd:

 struct iommufd_ucmd {
-       struct iommufd_ctx *ictx;
+       struct iommufd_ctx *ictx; /* Do not move; must be the first member */
        void __user *ubuffer;
        u32 user_size;
        void *cmd;
        struct iommufd_object *alloced_obj;
 };

Thanks
Nicolin