linux-kernel - RE: [PATCH v5 2/7] vfio/type1: Check reserve region conflict and update iova list

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Message-ID: <AADFC41AFE54684AB9EE6CBC0274A5D191085C0C@SHSMSX101.ccr.corp.intel.com>
Date:   Mon, 19 Mar 2018 12:16:22 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Shameerali Kolothum Thodi <shameerali.kolothum.thodi@...wei.com>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "eric.auger@...hat.com" <eric.auger@...hat.com>,
        "pmorel@...ux.vnet.ibm.com" <pmorel@...ux.vnet.ibm.com>
CC:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "xuwei (O)" <xuwei5@...wei.com>, Linuxarm <linuxarm@...wei.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>
Subject: RE: [PATCH v5 2/7] vfio/type1: Check reserve region conflict and
 update iova list

> From: Shameerali Kolothum Thodi
> [mailto:shameerali.kolothum.thodi@...wei.com]
> 
> > -----Original Message-----
> > From: Tian, Kevin [mailto:kevin.tian@...el.com]
> > Sent: Monday, March 19, 2018 7:52 AM
> > To: Shameerali Kolothum Thodi
> <shameerali.kolothum.thodi@...wei.com>;
> > alex.williamson@...hat.com; eric.auger@...hat.com;
> > pmorel@...ux.vnet.ibm.com
> > Cc: kvm@...r.kernel.org; linux-kernel@...r.kernel.org; xuwei (O)
> > <xuwei5@...wei.com>; Linuxarm <linuxarm@...wei.com>;
> > iommu@...ts.linux-foundation.org
> > Subject: RE: [PATCH v5 2/7] vfio/type1: Check reserve region conflict and
> > update iova list
> >
> > > From: Shameer Kolothum
> > > Sent: Friday, March 16, 2018 12:35 AM
> > >
> > > This retrieves the reserved regions associated with dev group and
> > > checks for conflicts with any existing dma mappings. Also update
> > > the iova list excluding the reserved regions.
> > >
> > > Signed-off-by: Shameer Kolothum
> > > <shameerali.kolothum.thodi@...wei.com>
> > > ---
> > >  drivers/vfio/vfio_iommu_type1.c | 90
> > > +++++++++++++++++++++++++++++++++++++++++
> > >  1 file changed, 90 insertions(+)
> > >
> > > diff --git a/drivers/vfio/vfio_iommu_type1.c
> > > b/drivers/vfio/vfio_iommu_type1.c
> > > index 1123c74..cfe2bb2 100644
> > > --- a/drivers/vfio/vfio_iommu_type1.c
> > > +++ b/drivers/vfio/vfio_iommu_type1.c
> > > @@ -1313,6 +1313,82 @@ static int vfio_iommu_aper_resize(struct
> > > list_head *iova,
> > >  	return 0;
> > >  }
> > >
> > > +/*
> > > + * Check reserved region conflicts with existing dma mappings
> > > + */
> > > +static bool vfio_iommu_resv_conflict(struct vfio_iommu *iommu,
> > > +				struct list_head *resv_regions)
> > > +{
> > > +	struct iommu_resv_region *region;
> > > +
> > > +	/* Check for conflict with existing dma mappings */
> > > +	list_for_each_entry(region, resv_regions, list) {
> > > +		if (vfio_find_dma(iommu, region->start, region->length))
> > > +			return true;
> > > +	}
> > > +
> > > +	return false;
> > > +}
> > > +
> > > +/*
> > > + * Check iova region overlap with  reserved regions and
> > > + * exclude them from the iommu iova range
> > > + */
> > > +static int vfio_iommu_resv_exclude(struct list_head *iova,
> > > +					struct list_head *resv_regions)
> > > +{
> > > +	struct iommu_resv_region *resv;
> > > +	struct vfio_iova *n, *next;
> > > +
> > > +	list_for_each_entry(resv, resv_regions, list) {
> > > +		phys_addr_t start, end;
> > > +
> > > +		start = resv->start;
> > > +		end = resv->start + resv->length - 1;
> > > +
> > > +		list_for_each_entry_safe(n, next, iova, list) {
> > > +			int ret = 0;
> > > +
> > > +			/* No overlap */
> > > +			if ((start > n->end) || (end < n->start))
> > > +				continue;
> > > +			/*
> > > +			 * Insert a new node if current node overlaps with
> > > the
> > > +			 * reserve region to exlude that from valid iova
> > > range.
> > > +			 * Note that, new node is inserted before the
> > > current
> > > +			 * node and finally the current node is deleted
> > > keeping
> > > +			 * the list updated and sorted.
> > > +			 */
> > > +			if (start > n->start)
> > > +				ret = vfio_iommu_iova_insert(&n->list,
> > > +							n->start, start - 1);
> > > +			if (!ret && end < n->end)
> > > +				ret = vfio_iommu_iova_insert(&n->list,
> > > +							end + 1, n->end);
> > > +			if (ret)
> > > +				return ret;
> >
> > Is it safer to delete the 1st node here in case of failure of the 2nd node?
> > There is no problem with current logic since upon error iova_copy will
> > be released anyway. However this function alone doesn't assume the
> > fact of a temporary list, thus it's better to keep the list clean w/o garbage
> > left from any error handling.
> 
> Agree. I will consider this.
> 
> > > +
> > > +			list_del(&n->list);
> > > +			kfree(n);
> > > +		}
> > > +	}
> > > +
> > > +	if (list_empty(iova))
> > > +		return -EINVAL;
> >
> > if list_empty should BUG_ON here? or do we really need this check?
> 
> I think we need the check here. This basically means there is no valid iova
> region as the reserved regions overlaps it completely(very unlikely, a bad
> configuration maybe). The __attach will fail if that happens and may be
> WARN_ON is a good idea to notify the user.
> 

you are right. I misread the code that deletion happens only
after insertion...

Thanks
Kevin