Re: [qemu-s390x] [PATCH 3/3] vfio-ccw: add handling for asnyc channel instructions

Cornelia Huck
2018-11-29T16:52:34Z

On Wed, 28 Nov 2018 17:36:04 +0100
Halil Pasic <pasic@linux.ibm.com> wrote:

> On Thu, 22 Nov 2018 17:54:32 +0100
> Cornelia Huck <cohuck@redhat.com> 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

> > +static size_t vfio_ccw_async_region_read(struct vfio_ccw_private *private,
> > + 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;
>
> I guess vfio_ccw_async_region_write() is supposed to be reentrant in a
> sense that there may be more that one 'instances' of the function
> executing at the same time, or am I wrong?
>
> If it is reenarant, I wonder what protects private->region[i].data from
> corruption or simply being changed 'while at it'?

Interesting question. AFAICS this same issue applies to the existing
I/O region as well.

There's nothing in common code enforcing any exclusivity. If I
understand the code correctly, the common vfio-pci code reads/writes in
1/2/4 byte chunks for most accesses. There's igd code that does not do
that, though.

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