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 <nicol...@nvidia.com>
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 <nicol...@nvidia.com>
Signed-off-by: Yi Liu <yi.l....@intel.com>
---
  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