Re: [PATCH 3/3] vfio-ccw: add handling for asnyc channel instructions

Cornelia Huck
2018-12-18T16:45:21Z

On Mon, 17 Dec 2018 16:54:31 -0500
Eric Farman <farman@linux.ibm.com> wrote:

> On 11/22/2018 11:54 AM, Cornelia Huck wrote:
> > Add a region to the vfio-ccw device that can be used to submit
> > asynchronous I/O instructions. ssch continues to be handled by the
> > existing I/O region; the new region handles hsch and csch.
> >
> > Interrupt status continues to be reported through the same channels
> > as for ssch.
> >
> > Signed-off-by: Cornelia Huck <cohuck@redhat.com>
> > ---
> > drivers/s390/cio/Makefile | 3 +-
> > drivers/s390/cio/vfio_ccw_async.c | 88 ++++++++++++++++
> > drivers/s390/cio/vfio_ccw_drv.c | 48 ++++++---
> > drivers/s390/cio/vfio_ccw_fsm.c | 158 +++++++++++++++++++++++++++-
> > drivers/s390/cio/vfio_ccw_ops.c | 13 ++-
> > drivers/s390/cio/vfio_ccw_private.h | 6 ++
> > include/uapi/linux/vfio.h | 4 +
> > include/uapi/linux/vfio_ccw.h | 12 +++
> > 8 files changed, 313 insertions(+), 19 deletions(-)
> > create mode 100644 drivers/s390/cio/vfio_ccw_async.c

> > diff --git a/drivers/s390/cio/vfio_ccw_async.c b/drivers/s390/cio/vfio_ccw_async.c
> > new file mode 100644
> > index 000000000000..8c7f51d17d70
> > --- /dev/null
> > +++ b/drivers/s390/cio/vfio_ccw_async.c
> > @@ -0,0 +1,88 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Async I/O region for vfio_ccw
> > + *
> > + * Copyright Red Hat, Inc. 2018
> > + *
> > + * Author(s): Cornelia Huck <cohuck@redhat.com>
> > + */
> > +
> > +#include <linux/vfio.h>
> > +#include <linux/mdev.h>
> > +
> > +#include "vfio_ccw_private.h"
> > +
> > +static size_t vfio_ccw_async_region_read(struct vfio_ccw_private *private,
>
> I think this should return ssize_t ? (same for _write, below)

Yes, ssize_t makes more sense. Changed.

(vfio_pci_regops also has size_t; should probably be changed as well.)

>
> > + char __user *buf, size_t count,
> > + loff_t *ppos)
> > +{
> > + unsigned int i = VFIO_CCW_OFFSET_TO_INDEX(*ppos) - VFIO_CCW_NUM_REGIONS;
> > + loff_t pos = *ppos & VFIO_CCW_OFFSET_MASK;
> > + struct ccw_cmd_region *region;
> > +
> > + if (pos + count > sizeof(*region))
> > + return -EINVAL;
> > +
> > + region = private->region[i].data;
> > + if (copy_to_user(buf, (void *)region + pos, count))
> > + return -EFAULT;
> > +
> > + return count;
> > +
> > +}
> > +
> > +static size_t vfio_ccw_async_region_write(struct vfio_ccw_private *private,
> > + const char __user *buf, size_t count,
> > + loff_t *ppos)
> > +{
> > + unsigned int i = VFIO_CCW_OFFSET_TO_INDEX(*ppos) - VFIO_CCW_NUM_REGIONS;
> > + loff_t pos = *ppos & VFIO_CCW_OFFSET_MASK;
> > + struct ccw_cmd_region *region;
> > +
> > + if (pos + count > sizeof(*region))
> > + return -EINVAL;
> > +
> > + if (private->state == VFIO_CCW_STATE_NOT_OPER ||
> > + private->state == VFIO_CCW_STATE_STANDBY)
> > + return -EACCES;
> > +
> > + region = private->region[i].data;
> > + if (copy_from_user((void *)region + pos, buf, count))
> > + return -EFAULT;
> > +
> > + switch (region->command) {
> > + case VFIO_CCW_ASYNC_CMD_HSCH:
> > + vfio_ccw_fsm_event(private, VFIO_CCW_EVENT_HALT_REQ);
> > + break;
> > + case VFIO_CCW_ASYNC_CMD_CSCH:
> > + vfio_ccw_fsm_event(private, VFIO_CCW_EVENT_CLEAR_REQ);
> > + break;
>
> I find myself wondering why we add separate VFIO_CCW_EVENT_x_REQ entries
> for HALT and CLEAR, rather than a single VFIO_CCW_EVENT_ASYNC_REQ and a
> switch on cmd_region->command within it to go to fsm_do_halt,
> fsm_do_clear, or whatever.

In the end, it probably does not matter much where we do the switch.
When I started writing this, I thought I would want to allow clear in
more states than halt; but that does not make much sense (best to let
the hardware sort it out; see also the other discussions around
concurrency.)

>
> > + default:
> > + return -EINVAL;
> > + }
> > +
> > + return region->ret_code ? region->ret_code : count;
> > +}

(...)

> > diff --git a/drivers/s390/cio/vfio_ccw_fsm.c b/drivers/s390/cio/vfio_ccw_fsm.c
> > index f94aa01f9c36..0caf77e8f377 100644
> > --- a/drivers/s390/cio/vfio_ccw_fsm.c
> > +++ b/drivers/s390/cio/vfio_ccw_fsm.c

> > @@ -102,6 +179,20 @@ static void fsm_io_busy(struct vfio_ccw_private *private,
> > private->io_region->ret_code = -EBUSY;
> > }
> >
> > +static void fsm_async_error(struct vfio_ccw_private *private,
> > + enum vfio_ccw_event event)
> > +{
> > + pr_err("vfio-ccw: FSM: halt/clear request from state:%d\n",
> > + private->state);
>
> Worth stating whether it's a Halt or Clear here, rather than leaving it
> ambiguous?

Not sure. Also not sure if we want to fold the events, as you suggested
above :)

This also reminds me that I need to rebase this: some details in the
handling will need to be different without the BOXED state.