On Mon, Oct 09, 2023 at 12:13:52PM +0800, Yi Liu wrote:
> 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.
I mean with this union, hwpt->auto_domain or hwpt->ioas should only be accessed if and
only if hwpt type is kernel-managed.
So, any unconditional access, as in iommufd_hw_pagetable_put() pasted below, is buggy.
Therefore, do you think it's better to add a filed like "bool kernel_managed : 1",
and access the union fields under /* kernel-managed */ only when hwpt->kernel_managed
is true.
>
> >
> > 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.
auto_domain is under union fields marked with kernel-managed only.
Access it without type checking is invalid.
struct iommufd_hw_pagetable {
struct iommufd_object obj;
struct iommu_domain *domain;
void (*abort)(struct iommufd_object *obj);
void (*destroy)(struct iommufd_object *obj);
bool user_managed : 1;
union {
struct { /* user-managed */
struct iommufd_hw_pagetable *parent;
};
struct { /* kernel-managed */
struct iommufd_ioas *ioas;
struct mutex mutex;
bool auto_domain : 1;
bool enforce_cache_coherency : 1;
bool msi_cookie : 1;
bool nest_parent : 1;
/* Head at iommufd_ioas::hwpt_list */
struct list_head hwpt_item;
};
};
};
>
> > 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
