On 01/30/2019 08:22 AM, Cornelia Huck wrote:
The flow for processing ssch requests can be improved by splitting
the BUSY state:
- CP_PROCESSING: We reject any user space requests while we are in
the process of translating a channel program and submitting it to
the hardware. Use -EAGAIN to signal user space that it should
retry the request.
- CP_PENDING: We have successfully submitted a request with ssch and
are now expecting an interrupt. As we can't handle more than one
channel program being processed, reject any further requests with
-EBUSY. A final interrupt will move us out of this state; this also
fixes a latent bug where a non-final interrupt might have freed up
a channel program that still was in progress.
By making this a separate state, we make it possible to issue a
halt or a clear while we're still waiting for the final interrupt
for the ssch (in a follow-on patch).
It also makes a lot of sense not to preemptively filter out writes to
the io_region if we're in an incorrect state: the state machine will
handle this correctly.
Signed-off-by: Cornelia Huck <address@hidden>
---
drivers/s390/cio/vfio_ccw_drv.c | 8 ++++++--
drivers/s390/cio/vfio_ccw_fsm.c | 19 ++++++++++++++-----
drivers/s390/cio/vfio_ccw_ops.c | 2 --
drivers/s390/cio/vfio_ccw_private.h | 3 ++-
4 files changed, 22 insertions(+), 10 deletions(-)
diff --git a/drivers/s390/cio/vfio_ccw_fsm.c b/drivers/s390/cio/vfio_ccw_fsm.c
index e7c9877c9f1e..b4a141fbd1a8 100644
--- a/drivers/s390/cio/vfio_ccw_fsm.c
+++ b/drivers/s390/cio/vfio_ccw_fsm.c
@@ -28,7 +28,6 @@ static int fsm_io_helper(struct vfio_ccw_private *private)
sch = private->sch;
spin_lock_irqsave(sch->lock, flags);
- private->state = VFIO_CCW_STATE_BUSY;
orb = cp_get_orb(&private->cp, (u32)(addr_t)sch, sch->lpm);
if (!orb) {
@@ -46,6 +45,7 @@ static int fsm_io_helper(struct vfio_ccw_private *private)
*/
sch->schib.scsw.cmd.actl |= SCSW_ACTL_START_PEND;
ret = 0;
+ private->state = VFIO_CCW_STATE_CP_PENDING;
[1]
break;
case 1: /* Status pending */
case 2: /* Busy */
@@ -107,6 +107,12 @@ static void fsm_io_busy(struct vfio_ccw_private *private,
private->io_region->ret_code = -EBUSY;
}
+static void fsm_io_retry(struct vfio_ccw_private *private,
+ enum vfio_ccw_event event)
+{
+ private->io_region->ret_code = -EAGAIN;
+}
+
static void fsm_disabled_irq(struct vfio_ccw_private *private,
enum vfio_ccw_event event)
{
@@ -135,8 +141,7 @@ static void fsm_io_request(struct vfio_ccw_private *private,
struct mdev_device *mdev = private->mdev;
char *errstr = "request";
- private->state = VFIO_CCW_STATE_BUSY;
-
+ private->state = VFIO_CCW_STATE_CP_PROCESSING;
[1]
memcpy(scsw, io_region->scsw_area, sizeof(*scsw));
if (scsw->cmd.fctl & SCSW_FCTL_START_FUNC) {
@@ -181,7 +186,6 @@ static void fsm_io_request(struct vfio_ccw_private *private,
}
err_out:
- private->state = VFIO_CCW_STATE_IDLE;
[1] Revisiting these locations as from an earlier discussion [2]...
These go IDLE->CP_PROCESSING->CP_PENDING if we get a cc=0 on the SSCH,
but we stop in CP_PROCESSING if the SSCH gets a nonzero cc. Shouldn't
we cleanup and go back to IDLE in this scenario, rather than forcing
userspace to escalate to CSCH/HSCH after some number of retries (via FSM)?
[2] https://patchwork.kernel.org/patch/10773611/#22447997