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SubjectRe: [PATCH v4 03/17] iommufd: Unite all kernel-managed members into a struct
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On 2023/10/9 13:13, Yan Zhao wrote:
> 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@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 <nicolinc@nvidia.com>
>>>> Signed-off-by: Yi Liu <yi.l.liu@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.
> I mean with this union, hwpt->auto_domain or hwpt->ioas should only be accessed if and
> only if hwpt type is kernel-managed.

ok, I get this part. just not sure about the missing words in your prior
comment.

> 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.

I see. yes, should check user_managed as well. :)

> 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

--
Regards,
Yi Liu

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