linux-kernel - RE: [PATCH v7 3/6] vfio/type1: Update iova list on detach

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Date:   Mon, 8 Jul 2019 07:10:51 +0000
From:   Shameerali Kolothum Thodi <shameerali.kolothum.thodi@...wei.com>
To:     Auger Eric <eric.auger@...hat.com>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>
CC:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        Linuxarm <linuxarm@...wei.com>,
        John Garry <john.garry@...wei.com>,
        "xuwei (O)" <xuwei5@...wei.com>,
        "kevin.tian@...el.com" <kevin.tian@...el.com>
Subject: RE: [PATCH v7 3/6] vfio/type1: Update iova list on detach

Hi Eric,

> -----Original Message-----
> From: Auger Eric [mailto:eric.auger@...hat.com]
> Sent: 07 July 2019 16:03
> To: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@...wei.com>;
> alex.williamson@...hat.com; pmorel@...ux.vnet.ibm.com
> Cc: kvm@...r.kernel.org; linux-kernel@...r.kernel.org;
> iommu@...ts.linux-foundation.org; Linuxarm <linuxarm@...wei.com>; John
> Garry <john.garry@...wei.com>; xuwei (O) <xuwei5@...wei.com>;
> kevin.tian@...el.com
> Subject: Re: [PATCH v7 3/6] vfio/type1: Update iova list on detach
> 
> Hi Shameer,
> 
> On 6/26/19 5:12 PM, Shameer Kolothum wrote:
> > Get a copy of iova list on _group_detach and try to update the list.
> > On success replace the current one with the copy. Leave the list as
> > it is if update fails.
> >
> > Signed-off-by: Shameer Kolothum <shameerali.kolothum.thodi@...wei.com>
> > ---
> >  drivers/vfio/vfio_iommu_type1.c | 91
> +++++++++++++++++++++++++++++++++
> >  1 file changed, 91 insertions(+)
> >
> > diff --git a/drivers/vfio/vfio_iommu_type1.c
> b/drivers/vfio/vfio_iommu_type1.c
> > index b6bfdfa16c33..e872fb3a0f39 100644
> > --- a/drivers/vfio/vfio_iommu_type1.c
> > +++ b/drivers/vfio/vfio_iommu_type1.c
> > @@ -1873,12 +1873,88 @@ static void vfio_sanity_check_pfn_list(struct
> vfio_iommu *iommu)
> >  	WARN_ON(iommu->notifier.head);
> >  }
> >
> > +/*
> > + * Called when a domain is removed in detach. It is possible that
> > + * the removed domain decided the iova aperture window. Modify the
> > + * iova aperture with the smallest window among existing domains.
> > + */
> > +static void vfio_iommu_aper_expand(struct vfio_iommu *iommu,
> > +				   struct list_head *iova_copy)
> Maybe you could just remove iova_copy for the args and return start,
> size. See comment below.
> > +{
> > +	struct vfio_domain *domain;
> > +	struct iommu_domain_geometry geo;
> > +	struct vfio_iova *node;
> > +	dma_addr_t start = 0;
> > +	dma_addr_t end = (dma_addr_t)~0;
> > +
> > +	list_for_each_entry(domain, &iommu->domain_list, next) {
> > +		iommu_domain_get_attr(domain->domain,
> DOMAIN_ATTR_GEOMETRY,
> > +				      &geo);
> > +		if (geo.aperture_start > start)
> > +			start = geo.aperture_start;
> > +		if (geo.aperture_end < end)
> > +			end = geo.aperture_end;
> > +	}
> > +
> > +	/* Modify aperture limits. The new aper is either same or bigger */
> > +	node = list_first_entry(iova_copy, struct vfio_iova, list);
> > +	node->start = start;
> > +	node = list_last_entry(iova_copy, struct vfio_iova, list);
> > +	node->end = end;
> > +}
> > +
> > +/*
> > + * Called when a group is detached. The reserved regions for that
> > + * group can be part of valid iova now. But since reserved regions
> > + * may be duplicated among groups, populate the iova valid regions
> > + * list again.
> > + */
> > +static int vfio_iommu_resv_refresh(struct vfio_iommu *iommu,
> > +				   struct list_head *iova_copy)
> > +{
> > +	struct vfio_domain *d;
> > +	struct vfio_group *g;
> > +	struct vfio_iova *node;
> > +	dma_addr_t start, end;
> > +	LIST_HEAD(resv_regions);
> > +	int ret;
> > +
> > +	list_for_each_entry(d, &iommu->domain_list, next) {
> > +		list_for_each_entry(g, &d->group_list, next)
> > +			iommu_get_group_resv_regions(g->iommu_group,
> > +						     &resv_regions);
> > +	}
> > +
> > +	if (list_empty(&resv_regions))
> > +		return 0;
> vfio_iommu_aper_expand() just extended the start/end of first & last
> node respectively.  In case the iova_copy() featured excluded resv
> regions before and now you don't have any anymore, the previous holes
> will stay if I don't miss anything?

Good catch!. Yes, I think there is a problem here.

> 
> You may unconditionally recompute start/end, free the copy,
> aper_resize() with new start/end and exclude resv regions again?

Ok. I will fix this in next revision.

Cheers,
Shameer