linux-kernel - Re: [PATCH v2 4/5] iommu: Support mm PASID 1:n with sva domains

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Date:   Mon, 28 Aug 2023 14:02:52 +0530
From:   Vasant Hegde <vasant.hegde@....com>
To:     Tina Zhang <tina.zhang@...el.com>, Jason Gunthorpe <jgg@...pe.ca>,
        Kevin Tian <kevin.tian@...el.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Michael Shavit <mshavit@...gle.com>
Cc:     iommu@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/5] iommu: Support mm PASID 1:n with sva domains

Hi Tina,

On 8/27/2023 2:14 PM, Tina Zhang wrote:
> Each mm bound to devices gets a PASID and corresponding sva domains
> allocated in iommu_sva_bind_device(), which are referenced by iommu_mm
> field of the mm. The PASID is released in __mmdrop(), while a sva domain
> is released when no one is using it (the reference count is decremented
> in iommu_sva_unbind_device()).
> 
> Since the required info of PASID and sva domains is kept in struct
> iommu_mm_data of a mm, use mm->iommu_mm field instead of the old pasid
> field in mm struct. The sva domain list is protected by iommu_sva_lock.
> 
> Besides, this patch removes mm_pasid_init(), as with the introduced
> iommu_mm structure, initializing mm pasid in mm_init() is unnecessary.
> 
> Signed-off-by: Tina Zhang <tina.zhang@...el.com>
> ---
>  drivers/iommu/iommu-sva.c | 38 +++++++++++++++++++++++++-------------
>  include/linux/iommu.h     | 10 +++-------
>  kernel/fork.c             |  1 -
>  3 files changed, 28 insertions(+), 21 deletions(-)
> 


.../...

>  
>  	/* Allocate a new domain and set it on device pasid. */
> @@ -105,6 +113,8 @@ struct iommu_sva *iommu_sva_bind_device(struct device *dev, struct mm_struct *mm
>  	if (ret)
>  		goto out_free_domain;
>  	domain->users = 1;
> +	list_add(&domain->next, &mm->iommu_mm->sva_domains);
> +
>  out:
>  	mutex_unlock(&iommu_sva_lock);
>  	handle->dev = dev;
> @@ -137,8 +147,9 @@ void iommu_sva_unbind_device(struct iommu_sva *handle)
>  	struct device *dev = handle->dev;
>  
>  	mutex_lock(&iommu_sva_lock);
> +	iommu_detach_device_pasid(domain, dev, pasid);
>  	if (--domain->users == 0) {
> -		iommu_detach_device_pasid(domain, dev, pasid);
> +		list_del(&domain->next);
>  		iommu_domain_free(domain);
>  	}
>  	mutex_unlock(&iommu_sva_lock);
> @@ -218,4 +229,5 @@ void mm_pasid_drop(struct mm_struct *mm)
>  		return;
>  
>  	ida_free(&iommu_global_pasid_ida, mm_get_pasid(mm));
> +	kfree(mm->iommu_mm);


I am not sure whether I understood the flow completely. Just wondering why you
are not freeing pasid in iommu_sva_unbind_device().
I mean once iommu_mm->sva_domains becomes free shouldn't we free the
iommu_mm->pasid?

Also in this function (mm_pasid_drop()), should we check/free sva domains?

-Vasant