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

[Yi Liu]

On 2023/10/7 18:08, Yan Zhao wrote:
> 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?

yes.

> 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.

not quite get this sentence.

>   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);

this is true. this assert is not needed when hwpt is not kernel managed domain.

> +
> +       if (!hwpt->user_managed && hwpt->auto_domain)

actually, checking auto_domain is more precise. There is hwpt which is 
neither user managed nor auto.

>                  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

--
Regards,
Yi Liu