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

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Date:   Mon, 9 Oct 2023 12:13:52 +0800
From:   Yi Liu <yi.l.liu@...el.com>
To:     Yan Zhao <yan.y.zhao@...el.com>
CC:     <joro@...tes.org>, <alex.williamson@...hat.com>, <jgg@...dia.com>,
        <kevin.tian@...el.com>, <robin.murphy@....com>,
        <baolu.lu@...ux.intel.com>, <cohuck@...hat.com>,
        <eric.auger@...hat.com>, <nicolinc@...dia.com>,
        <kvm@...r.kernel.org>, <mjrosato@...ux.ibm.com>,
        <chao.p.peng@...ux.intel.com>, <yi.y.sun@...ux.intel.com>,
        <peterx@...hat.com>, <jasowang@...hat.com>,
        <shameerali.kolothum.thodi@...wei.com>, <lulu@...hat.com>,
        <suravee.suthikulpanit@....com>, <iommu@...ts.linux.dev>,
        <linux-kernel@...r.kernel.org>, <linux-kselftest@...r.kernel.org>,
        <zhenzhong.duan@...el.com>, <joao.m.martins@...cle.com>
Subject: Re: [PATCH v4 03/17] iommufd: Unite all kernel-managed members into a
 struct

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@...dia.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@...dia.com>
>> Signed-off-by: Yi Liu <yi.l.liu@...el.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