[RFC PATCH v2 3/4] vfio-ccw: Expand SCSW usage to HALT and CLEAR

Eric Farman
2020-05-13T14:29:43Z

Expand the Activity Control flags to include HALT/CLEAR PENDING,
in the same way as is done for the START PENDING flag.

The POPS states that for HALT SUBCHANNEL:

> Condition code 2 is set, and no other action is
> taken, ... when a halt function or clear function is
> already in progress at the subchannel.

So take that into account in fsm_do_halt().

CLEAR SUBCHANNEL is the biggest hammer, and always gets to happen,
so no corresponding check is added to fsm_do_clear(). But it does
reset both START and HALT functions that may be active, which is
why it incorporates the resetting of the HALT bit on the interrupt
path.

FIXME: What happens if a guest hammers a bunch of CSCH in a row?
We clear this for the first interrupt; is that fine?

Signed-off-by: Eric Farman <farman@linux.ibm.com>
---
drivers/s390/cio/vfio_ccw_drv.c | 6 ++++++
drivers/s390/cio/vfio_ccw_fsm.c | 12 +++++++++++-
2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/drivers/s390/cio/vfio_ccw_drv.c b/drivers/s390/cio/vfio_ccw_drv.c
index ee153fa72a0f..55051972325f 100644
--- a/drivers/s390/cio/vfio_ccw_drv.c
+++ b/drivers/s390/cio/vfio_ccw_drv.c
@@ -101,6 +101,12 @@ static void vfio_ccw_sch_io_todo(struct work_struct *work)
if (private->mdev && scsw_is_solicited(&irb->scsw) && is_final) {
private->state = VFIO_CCW_STATE_IDLE;
private->scsw.cmd.actl &= ~SCSW_ACTL_START_PEND;
+ if (scsw_fctl(&irb->scsw) & SCSW_FCTL_HALT_FUNC)
+ private->scsw.cmd.actl &= ~SCSW_ACTL_HALT_PEND;
+ if (scsw_fctl(&irb->scsw) & SCSW_FCTL_CLEAR_FUNC) {
+ private->scsw.cmd.actl &= ~SCSW_ACTL_HALT_PEND;
+ private->scsw.cmd.actl &= ~SCSW_ACTL_CLEAR_PEND;
+ }
}

if (private->io_trigger)
diff --git a/drivers/s390/cio/vfio_ccw_fsm.c b/drivers/s390/cio/vfio_ccw_fsm.c
index 258ce32549f3..d8075a56eb9b 100644
--- a/drivers/s390/cio/vfio_ccw_fsm.c
+++ b/drivers/s390/cio/vfio_ccw_fsm.c
@@ -86,6 +86,14 @@ static int fsm_do_halt(struct vfio_ccw_private *private)

sch = private->sch;

+ if (scsw_actl(&private->scsw) & (SCSW_ACTL_HALT_PEND | SCSW_ACTL_CLEAR_PEND)) {
+ VFIO_CCW_MSG_EVENT(2,
+ "%pUl: actl %x pending\n",
+ mdev_uuid(private->mdev),
+ scsw_actl(&private->scsw));
+ return -EBUSY;
+ }
+
spin_lock_irqsave(sch->lock, flags);

VFIO_CCW_TRACE_EVENT(2, "haltIO");
@@ -102,6 +110,7 @@ static int fsm_do_halt(struct vfio_ccw_private *private)
* Initialize device status information
*/
sch->schib.scsw.cmd.actl |= SCSW_ACTL_HALT_PEND;
+ private->scsw.cmd.actl |= SCSW_ACTL_HALT_PEND;
ret = 0;
break;
case 1: /* Status pending */
@@ -143,6 +152,7 @@ static int fsm_do_clear(struct vfio_ccw_private *private)
* Initialize device status information
*/
sch->schib.scsw.cmd.actl = SCSW_ACTL_CLEAR_PEND;
+ private->scsw.cmd.actl |= SCSW_ACTL_CLEAR_PEND;
/* TODO: check what else we might need to clear */
ret = 0;
break;
@@ -246,7 +256,7 @@ static void fsm_io_request(struct vfio_ccw_private *private,
char *errstr = "request";
struct subchannel_id schid = get_schid(private);

- if (scsw_actl(scsw) & SCSW_ACTL_START_PEND) {
+ if (scsw_actl(scsw) & (SCSW_ACTL_START_PEND | SCSW_ACTL_HALT_PEND | SCSW_ACTL_CLEAR_PEND)) {
io_region->ret_code = -EBUSY;
VFIO_CCW_MSG_EVENT(2,
"%pUl (%x.%x.%04x): actl %x pending\n",
--
2.17.1