linux-kernel - Re: [RFC v3 1/8] vfio: Add VFIO_IOMMU_PASID

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Message-ID: <20200206101253.7fb43e07@jacob-builder>
Date:   Thu, 6 Feb 2020 10:12:53 -0800
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     "Liu, Yi L" <yi.l.liu@...el.com>
Cc:     Alex Williamson <alex.williamson@...hat.com>,
        "eric.auger@...hat.com" <eric.auger@...hat.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Tian, Jun J" <jun.j.tian@...el.com>,
        "Sun, Yi Y" <yi.y.sun@...el.com>,
        "jean-philippe.brucker@....com" <jean-philippe.brucker@....com>,
        "peterx@...hat.com" <peterx@...hat.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        jacob.jun.pan@...ux.intel.com
Subject: Re: [RFC v3 1/8] vfio: Add VFIO_IOMMU_PASID_REQUEST(alloc/free)

Hi Alex,

On Fri, 31 Jan 2020 12:41:06 +0000
"Liu, Yi L" <yi.l.liu@...el.com> wrote:

> > > +static int vfio_iommu_type1_pasid_free(struct vfio_iommu *iommu,
> > > +				       unsigned int pasid)
> > > +{
> > > +	struct vfio_mm *vmm = iommu->vmm;
> > > +	int ret = 0;
> > > +
> > > +	mutex_lock(&iommu->lock);
> > > +	if (!IS_IOMMU_CAP_DOMAIN_IN_CONTAINER(iommu)) {  
> > 
> > But we could have been IOMMU backed when the pasid was allocated,
> > did we just leak something?  In fact, I didn't spot anything in
> > this series that handles a container with pasids allocated losing
> > iommu backing. I'd think we want to release all pasids when that
> > happens since permission for the user to hold pasids goes along
> > with having an iommu backed device.  
> 
> oh, yes. If a container lose iommu backend, then needs to reclaim the
> allocated PASIDs. right? I'll add it. :-)
> 
> > Also, do we want _free() paths that can fail?  
> 
> I remember we discussed if a _free() path can fail, I think we agreed
> to let _free() path always success. :-)

Just to add some details. We introduced IOASID notifier such that when
VFIO frees a PASID, consumers such as IOMMU, can do the cleanup
therefore ensure free always succeeds.
https://www.spinics.net/lists/kernel/msg3349928.html
https://www.spinics.net/lists/kernel/msg3349930.html
This was not in my v9 set as I was considering some race conditions
w.r.t. registering notifier, gets notifications, and free call. I will
post it in v10.

Thanks,

Jacob