Re: [PATCH v4 03/17] iommufd: Unite all kernel-managed members into a struct

[Yan Zhao]

On Thu, Sep 21, 2023 at 12:51:24AM -0700, Yi Liu wrote:
> From: Nicolin Chen <nicolinc@xxxxxxxxxx>
> 
> The struct iommufd_hw_pagetable has been representing a kernel-managed
> HWPT, yet soon will be reused to represent a user-managed HWPT. These
> two types of HWPTs has the same IOMMUFD object type and an iommu_domain
> object, but have quite different attributes/members.
> 
> Add a union in struct iommufd_hw_pagetable and group all the existing
> kernel-managed members. One of the following patches will add another
> struct for user-managed members.
> 
> Signed-off-by: Nicolin Chen <nicolinc@xxxxxxxxxx>
> Signed-off-by: Yi Liu <yi.l.liu@xxxxxxxxx>
> ---
>  drivers/iommu/iommufd/iommufd_private.h | 17 +++++++++++------
>  1 file changed, 11 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/iommu/iommufd/iommufd_private.h b/drivers/iommu/iommufd/iommufd_private.h
> index 3064997a0181..947a797536e3 100644
> --- a/drivers/iommu/iommufd/iommufd_private.h
> +++ b/drivers/iommu/iommufd/iommufd_private.h
> @@ -231,13 +231,18 @@ int iommufd_vfio_ioas(struct iommufd_ucmd *ucmd);
>   */
>  struct iommufd_hw_pagetable {
>  	struct iommufd_object obj;
> -	struct iommufd_ioas *ioas;
>  	struct iommu_domain *domain;
> -	bool auto_domain : 1;
> -	bool enforce_cache_coherency : 1;
> -	bool msi_cookie : 1;
> -	/* Head at iommufd_ioas::hwpt_list */
> -	struct list_head hwpt_item;
> +
> +	union {
> +		struct { /* kernel-managed */
> +			struct iommufd_ioas *ioas;
> +			bool auto_domain : 1;
Will iommufd_hw_pagetable_put() also be called on non-kernel-managed domain?
If yes, hwpt->user_managed needs to be checked in iommufd_hw_pagetable_put(),
(e.g. as below).
Otherwise, this union will lead to hwpt->ioas and hwpt->auto_domain still being
accessible though invalid.


 static inline void iommufd_hw_pagetable_put(struct iommufd_ctx *ictx,
                                            struct iommufd_hw_pagetable *hwpt)
 {
-       lockdep_assert_not_held(&hwpt->ioas->mutex);
-       if (hwpt->auto_domain)
+       if (!hwpt->user_managed)
+               lockdep_assert_not_held(&hwpt->ioas->mutex);
+
+       if (!hwpt->user_managed && hwpt->auto_domain)
                iommufd_object_deref_user(ictx, &hwpt->obj);
        else
                refcount_dec(&hwpt->obj.users);
}

> +			bool enforce_cache_coherency : 1;
> +			bool msi_cookie : 1;
> +			/* Head at iommufd_ioas::hwpt_list */
> +			struct list_head hwpt_item;
> +		};
> +	};
>  };
>  
>  struct iommufd_hw_pagetable *
> -- 
> 2.34.1
>