Re: [PATCH v5 03/13] iommufd: Add iommufd_verify_unfinalized_object

[Jason Gunthorpe]

On Fri, Oct 25, 2024 at 04:49:43PM -0700, Nicolin Chen wrote:
> To support driver-allocated vIOMMU objects, it's suggested to call the
> allocator helper in IOMMU dirvers. However, there is no guarantee that
> drivers will all use it and allocate objects properly.
> 
> Add a helper for iommufd core to verify if an unfinalized object is at
> least reserved in the ictx.

I don't think we need this..

iommufd_object_finalize() already does:

        old = xa_store(&ictx->objects, obj->id, obj, GFP_KERNEL);
        /* obj->id was returned from xa_alloc() so the xa_store() cannot fail */
        WARN_ON(old);

So, we could enhance it to be more robust, like this patch is doing:

void iommufd_object_finalize(struct iommufd_ctx *ictx,
                             struct iommufd_object *obj)
{
        void *old;

        old = xa_cmpxchg(&ictx->objects, obj->id, XA_ZERO_ENTRY, obj,
                         GFP_KERNEL);
        /* obj->id was returned from xa_alloc() so the xa_store() cannot fail */
        WARN_ON(old != XA_ZERO_ENTRY);

It is always a driver bug to not initialize that object, so WARN_ON is
OK.

Jason