From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jacob Pan <jacob.jun.pan-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
Subject: Re: [PATCH V4 05/18] iommu/ioasid: Redefine IOASID set and
 allocation APIs
Date: Thu, 18 Mar 2021 17:22:34 -0700
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To: LKML <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Joerg Roedel <joro-zLv9SwRftAIdnm+yROfE0A@public.gmane.org>, Lu
 Baolu <baolu.lu-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>, David Woodhouse <dwmw2-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>, iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, Li Zefan <lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>, Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>, Jean-Philippe Brucker <jean-philippe-68IGFXMjmZ7QT0dZR+AlfA@public.gmane.org>
Cc: "Tian, Kevin" <kevin.tian-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>, Dave Jiang <dave.jiang-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>, Raj Ashok <ashok.raj-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>, Jonathan Corbet <corbet-T1hC0tSOHrs@public.gmane.org>, Alex Williamson <alex.williamson-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Jason Gunthorpe <jgg-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>, Wu Hao <hao.wu-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>

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