linux-kernel - RE: [PATCH v5 0/7] vfio/type1: Add support for valid iova list management

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Message-ID: <AADFC41AFE54684AB9EE6CBC0274A5D191085BED@SHSMSX101.ccr.corp.intel.com>
Date:   Mon, 19 Mar 2018 12:12:47 +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 0/7] vfio/type1: Add support for valid iova list
 management

> From: Shameerali Kolothum Thodi
> [mailto:shameerali.kolothum.thodi@...wei.com]
> 
> Hi Kevin,
> 
> Thanks for taking a look at this series.
> 
> > -----Original Message-----
> > From: Tian, Kevin [mailto:kevin.tian@...el.com]
> > Sent: Monday, March 19, 2018 8:29 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 0/7] vfio/type1: Add support for valid iova list
> > management
> >
> > > From: Shameer Kolothum
> > > Sent: Friday, March 16, 2018 12:35 AM
> > >
> > > This series introduces an iova list associated with a vfio
> > > iommu. The list is kept updated taking care of iommu apertures,
> > > and reserved regions. Also this series adds checks for any conflict
> > > with existing dma mappings whenever a new device group is attached
> to
> > > the domain.
> > >
> > > User-space can retrieve valid iova ranges using
> VFIO_IOMMU_GET_INFO
> > > ioctl capability chains. Any dma map request outside the valid iova
> > > range will be rejected.
> >
> > GET_INFO is done at initialization time which is good for cold attached
> > devices. If a hotplugged device may cause change of valid iova ranges
> > at run-time, then there could be potential problem (which however is
> > difficult for user space or orchestration stack to figure out in advance)
> > Can we do some extension like below to make hotplug case cleaner?
> 
> As I understand, in case a hotplugged device results in an update to the
> valid
> Iova ranges then the Qemu, vfio_connect_container() -->
> memory_listner_register()
> will fail if there is a conflict as patch #4 checks for invalid dma map requests.

OK, possibly Qemu can do another GET_INFO upon any dma map 
error to get latest ranges and then allocate a new valid iova to
redo the map. this should work if valid ranges shrink due to new
hotplugged device. But if hot-removing a device may result in
more valid ranges, so far there is no way for Qemu to pick up.
I'm not sure whether we want to go that far though...

> 
> Not sure, your concern is preventing hotplug much before this happens or
> not.
> 

yes, my earlier thought is more to catch the problem in attach phase.

Thanks
Kevin