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

Nicolin Chen
2025-05-16T20:56:50Z

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