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Date:   Thu, 18 Mar 2021 17:22:34 -0700
From:   Jacob Pan <jacob.jun.pan@linux.intel.com>
To:     LKML <linux-kernel@vger.kernel.org>,
        Joerg Roedel <joro@8bytes.org>,
        "Lu Baolu" <baolu.lu@linux.intel.com>,
        David Woodhouse <dwmw2@infradead.org>,
        iommu@lists.linux-foundation.org, cgroups@vger.kernel.org,
        Tejun Heo <tj@kernel.org>, Li Zefan <lizefan@huawei.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Jean-Philippe Brucker <jean-philippe@linaro.com>
Cc:     Alex Williamson <alex.williamson@redhat.com>,
        Eric Auger <eric.auger@redhat.com>,
        Jason Gunthorpe <jgg@nvidia.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Raj Ashok <ashok.raj@intel.com>,
        "Tian, Kevin" <kevin.tian@intel.com>, Yi Liu <yi.l.liu@intel.com>,
        Wu Hao <hao.wu@intel.com>, Dave Jiang <dave.jiang@intel.com>,
        jacob.jun.pan@linux.intel.com
Subject: Re: [PATCH V4 05/18] iommu/ioasid: Redefine IOASID set and
 allocation APIs
Message-ID: <20210318172234.3e8c34f7@jacob-builder>
In-Reply-To: <1614463286-97618-6-git-send-email-jacob.jun.pan@linux.intel.com>
References: <1614463286-97618-1-git-send-email-jacob.jun.pan@linux.intel.com>
        <1614463286-97618-6-git-send-email-jacob.jun.pan@linux.intel.com>
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Hi Jean,

Slightly off the title. As we are moving to use cgroup to limit PASID
allocations, it would be much simpler if we enforce on the current task.

However, iommu_sva_alloc_pasid() takes an mm_struct pointer as argument
which implies it can be something other the the current task mm. So far all
kernel callers use current task mm. Is there a use case for doing PASID
allocation on behalf of another mm? If not, can we remove the mm argument?

Thanks,

Jacob

>  /**
>   * iommu_sva_alloc_pasid - Allocate a PASID for the mm
> @@ -35,11 +44,11 @@ int iommu_sva_alloc_pasid(struct mm_struct *mm,
> ioasid_t min, ioasid_t max) mutex_lock(&iommu_sva_lock);
>  	if (mm->pasid) {
>  		if (mm->pasid >= min && mm->pasid <= max)
> -			ioasid_get(mm->pasid);
> +			ioasid_get(iommu_sva_pasid, mm->pasid);
>  		else
>  			ret = -EOVERFLOW;
>  	} else {
> -		pasid = ioasid_alloc(&iommu_sva_pasid, min, max, mm);
> +		pasid = ioasid_alloc(iommu_sva_pasid, min, max, mm);
>  		if (pasid == INVALID_IOASID)
>  			ret = -ENOMEM;

Thanks,

Jacob