Date:   Mon, 6 May 2019 23:22:35 +0000
From:   Parav Pandit <parav@...lanox.com>
To:     Alex Williamson <alex.williamson@...hat.com>
CC:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kwankhede@...dia.com" <kwankhede@...dia.com>,
        "cjia@...dia.com" <cjia@...dia.com>
Subject: RE: [PATCHv2 00/10] vfio/mdev: Improve vfio/mdev core module



> -----Original Message-----
> From: Alex Williamson <alex.williamson@...hat.com>
> Sent: Monday, May 6, 2019 5:03 PM
> To: Parav Pandit <parav@...lanox.com>
> Cc: kvm@...r.kernel.org; linux-kernel@...r.kernel.org;
> kwankhede@...dia.com; cjia@...dia.com
> Subject: Re: [PATCHv2 00/10] vfio/mdev: Improve vfio/mdev core module
> 
> On Tue, 30 Apr 2019 17:49:27 -0500
> Parav Pandit <parav@...lanox.com> wrote:
> 
> > As we would like to use mdev subsystem for wider use case as discussed
> > in [1], [2] apart from an offline discussion.
> > This use case is also discussed with wider forum in [4] in track
> > 'Lightweight NIC HW functions for container offload use cases'.
> >
> > This series is prep-work and improves vfio/mdev module in following ways.
> >
> > Patch-1 Fixes releasing parent dev reference during error unwinding
> >         mdev parent registration.
> > Patch-2 Simplifies mdev device for unused kref.
> > Patch-3 Drops redundant extern prefix of exported symbols.
> > Patch-4 Returns right error code from vendor driver.
> > Patch-5 Fixes to use right sysfs remove sequence.
> > Patch-6 Fixes removing all child devices if one of them fails.
> > Patch-7 Remove unnecessary inline
> > Patch-8 Improve the mdev create/remove sequence to match Linux
> >         bus, device model
> > Patch-9 Avoid recreating remove file on stale device to
> >         eliminate call trace
> > Patch-10 Fix race conditions of create/remove with parent removal This
> > is improved version than using srcu as srcu can take seconds to
> > minutes.
> >
> > This series is tested using
> > (a) mtty with VM using vfio_mdev driver for positive tests and device
> > removal while device in use by VM using vfio_mdev driver
> >
> > (b) mlx5 core driver using RFC patches [3] and internal patches.
> > Internal patches are large and cannot be combined with this prep-work
> > patches. It will posted once prep-work completes.
> >
> > [1] https://www.spinics.net/lists/netdev/msg556978.html
> > [2] https://lkml.org/lkml/2019/3/7/696
> > [3] https://lkml.org/lkml/2019/3/8/819
> > [4] https://netdevconf.org/0x13/session.html?workshop-hardware-offload
> >
> > ---
> > Changelog:
> > ---
> > v1->v2:
> >  - Addressed comments from Alex
> >  - Rebased
> >  - Inserted the device checking loop in Patch-6 as original code
> >  - Added patch 7 to 10
> >  - Added fixes for race condition in create/remove with parent removal
> >    Patch-10 uses simplified refcount and completion, instead of srcu
> >    which might take seconds to minutes on busy system.
> >  - Added fix for device create/remove sequence to match
> >    Linux device, bus model
> > v0->v1:
> >  - Dropped device placement on bus sequence patch for this series
> >  - Addressed below comments from Alex, Kirti, Maxim.
> >  - Added Review-by tag for already reviewed patches.
> >  - Dropped incorrect patch of put_device().
> >  - Corrected Fixes commit tag for sysfs remove sequence fix
> >  - Split last 8th patch to smaller refactor and fixes patch
> >  - Following coding style commenting format
> >  - Fixed accidental delete of mutex_lock in mdev_unregister_device
> >  - Renamed remove helped to mdev_device_remove_common().
> >  - Rebased for uuid/guid change
> >
> > Parav Pandit (10):
> >   vfio/mdev: Avoid release parent reference during error path
> >   vfio/mdev: Removed unused kref
> >   vfio/mdev: Drop redundant extern for exported symbols
> >   vfio/mdev: Avoid masking error code to EBUSY
> >   vfio/mdev: Follow correct remove sequence
> >   vfio/mdev: Fix aborting mdev child device removal if one fails
> >   vfio/mdev: Avoid inline get and put parent helpers
> >   vfio/mdev: Improve the create/remove sequence
> >   vfio/mdev: Avoid creating sysfs remove file on stale device removal
> >   vfio/mdev: Synchronize device create/remove with parent removal
> >
> >  drivers/vfio/mdev/mdev_core.c    | 162 +++++++++++++------------------
> >  drivers/vfio/mdev/mdev_private.h |   9 +-
> >  drivers/vfio/mdev/mdev_sysfs.c   |   8 +-
> >  include/linux/mdev.h             |  21 ++--
> >  4 files changed, 89 insertions(+), 111 deletions(-)
> >
> 
> Hi Parav,
> 
> I applied 1-7 to the vfio next branch for v5.2 since these are mostly
> previously reviewed or trivial.  I'm not ruling out the rest for v5.2 as bug fixes
> yet, but they require a bit more to digest and hopefully we'll get some
> feedback from others as well.  Thanks,
> 
Ok. Great.
Yes, these are important for us to make use of mdev.
We should address them in 5.2 window.
I will look for any comments this week and address them as required.

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