linux-kernel - Re: [PATCH V4 05/18] iommu/ioasid: Redefine IOASID set and allocation APIs

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Message-ID: <20210318172234.3e8c34f7@jacob-builder>
Date:   Thu, 18 Mar 2021 17:22:34 -0700
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        "Lu Baolu" <baolu.lu@...ux.intel.com>,
        David Woodhouse <dwmw2@...radead.org>,
        iommu@...ts.linux-foundation.org, cgroups@...r.kernel.org,
        Tejun Heo <tj@...nel.org>, Li Zefan <lizefan@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>
Cc:     Alex Williamson <alex.williamson@...hat.com>,
        Eric Auger <eric.auger@...hat.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Jonathan Corbet <corbet@....net>,
        Raj Ashok <ashok.raj@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>, Yi Liu <yi.l.liu@...el.com>,
        Wu Hao <hao.wu@...el.com>, Dave Jiang <dave.jiang@...el.com>,
        jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH V4 05/18] iommu/ioasid: Redefine IOASID set and
 allocation APIs

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