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Re: [Qemu-devel] [PATCH v3 0/6] vfio-ccw: support hsch/csch (kernel part

From: Eric Farman
Subject: Re: [Qemu-devel] [PATCH v3 0/6] vfio-ccw: support hsch/csch (kernel part)
Date: Fri, 8 Feb 2019 16:19:58 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1

On 02/06/2019 09:00 AM, Cornelia Huck wrote:
On Wed, 30 Jan 2019 14:22:06 +0100
Cornelia Huck <address@hidden> wrote:

[This is the Linux kernel part, git tree is available at

I've pushed out the changes I've made so far (patch 1) to
vfio-ccw-eagain-caps-v3.5. I'll wait a bit for more comments before
sending a new version.

Thanks for that branch...  For patch 1 in v3.5:

Reviewed-by: Eric Farman <address@hidden>

The companion QEMU patches are available at
https://github.com/cohuck/qemu vfio-ccw-caps
This is the previously posted v2 version, which should continue to work.]

I would not mind if somebody looked at those as well :)

Not precluding anyone else from doing so :) ... I'd planned on looking at them as I get into the meat of patches 4-6 on the kernel side, where the overlap occurs. I'm getting close. :)

FWIW, I've been running with both series for the last week or two, along with some host kernel traces to prove things got executed the way I thought, and it's seemed to be working well. So that makes me optimistic for the later patches.

 - Eric

Currently, vfio-ccw only relays START SUBCHANNEL requests to the real
device. This tends to work well for the most common 'good path' scenarios;
however, as we emulate {HALT,CLEAR} SUBCHANNEL in QEMU, things like
clearing pending requests at the device is currently not supported.
This may be a problem for e.g. error recovery.

This patch series introduces capabilities (similar to what vfio-pci uses)
and exposes a new async region for handling hsch/csch.

Lightly tested (I can interact with a dasd as before, and reserve/release
seems to work well.) Not sure if there is a better way to test this, ideas

Changes v2->v3:
- Unb0rked patch 1, improved scope
- Split out the new mutex from patch 2 into new patch 3; added missing
   locking and hopefully improved description
- Patch 2 now reworks the state handling by splitting the BUSY state
- Patches 3 and 5 adapted on top of the reworked patches; hsch/csch
   are allowed in CP_PENDING, but not in CP_PROCESSING (did not add
   any R-b due to that)
- Added missing free in patch 5
- Probably some small changes I forgot to note down

Changes v1->v2:
- New patch 1: make it safe to use the cp accessors at any time; this
   should avoid problems with unsolicited interrupt handling
- New patch 2: handle concurrent accesses to the io region; the idea is
   to return -EAGAIN to userspace more often (so it can simply retry)
- also handle concurrent accesses to the async io region
- merge events for halt and clear to a single async event; this turned out
   to make the code quite a bit simpler
- probably some small changes I forgot to note down

Cornelia Huck (6):
   vfio-ccw: make it safe to access channel programs
   vfio-ccw: rework ssch state handling
   vfio-ccw: protect the I/O region
   vfio-ccw: add capabilities chain
   s390/cio: export hsch to modules
   vfio-ccw: add handling for async channel instructions

  drivers/s390/cio/Makefile           |   3 +-
  drivers/s390/cio/ioasm.c            |   1 +
  drivers/s390/cio/vfio_ccw_async.c   |  88 ++++++++++++
  drivers/s390/cio/vfio_ccw_cp.c      |  20 ++-
  drivers/s390/cio/vfio_ccw_cp.h      |   2 +
  drivers/s390/cio/vfio_ccw_drv.c     |  57 ++++++--
  drivers/s390/cio/vfio_ccw_fsm.c     | 143 ++++++++++++++++++-
  drivers/s390/cio/vfio_ccw_ops.c     | 210 +++++++++++++++++++++++-----
  drivers/s390/cio/vfio_ccw_private.h |  48 ++++++-
  include/uapi/linux/vfio.h           |   4 +
  include/uapi/linux/vfio_ccw.h       |  12 ++
  11 files changed, 531 insertions(+), 57 deletions(-)
  create mode 100644 drivers/s390/cio/vfio_ccw_async.c

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