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Re: [qemu-s390x] [RFC PATCH 1/3] vfio: ccw: introduce schib region

From: Pierre Morel
Subject: Re: [qemu-s390x] [RFC PATCH 1/3] vfio: ccw: introduce schib region
Date: Mon, 15 Jan 2018 10:50:00 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.0 
On 11/01/2018 04:04, Dong Jia Shi wrote:

This introduces a new region for vfio-ccw to provide subchannel
information for user space.

Signed-off-by: Dong Jia Shi <address@hidden>
---
  drivers/s390/cio/vfio_ccw_fsm.c     | 21 ++++++++++
  drivers/s390/cio/vfio_ccw_ops.c     | 79 +++++++++++++++++++++++++++----------
  drivers/s390/cio/vfio_ccw_private.h |  3 ++
  include/uapi/linux/vfio.h           |  1 +
  include/uapi/linux/vfio_ccw.h       |  6 +++
  5 files changed, 90 insertions(+), 20 deletions(-)

diff --git a/drivers/s390/cio/vfio_ccw_fsm.c b/drivers/s390/cio/vfio_ccw_fsm.c
index c30420c517b1..be081ccabea3 100644
--- a/drivers/s390/cio/vfio_ccw_fsm.c
+++ b/drivers/s390/cio/vfio_ccw_fsm.c
@@ -172,6 +172,22 @@ static void fsm_irq(struct vfio_ccw_private *private,
                complete(private->completion);
  }

+static void fsm_update_subch(struct vfio_ccw_private *private,
+                            enum vfio_ccw_event event)
+{
+       struct subchannel *sch;
+
+       sch = private->sch;
+       if (cio_update_schib(sch)) {
+               private->schib_region.cc = 3;
+               return;
+       }
+
+       private->schib_region.cc = 0;
+       memcpy(private->schib_region.schib_area, &sch->schib,
+              sizeof(sch->schib));
+}
+
  /*
   * Device statemachine
   */
@@ -180,25 +196,30 @@ fsm_func_t 
*vfio_ccw_jumptable[NR_VFIO_CCW_STATES][NR_VFIO_CCW_EVENTS] = {
                [VFIO_CCW_EVENT_NOT_OPER]       = fsm_nop,
                [VFIO_CCW_EVENT_IO_REQ]         = fsm_io_error,
                [VFIO_CCW_EVENT_INTERRUPT]      = fsm_disabled_irq,
+               [VFIO_CCW_EVENT_UPDATE_SUBCH]   = fsm_update_subch,
        },
        [VFIO_CCW_STATE_STANDBY] = {
                [VFIO_CCW_EVENT_NOT_OPER]       = fsm_notoper,
                [VFIO_CCW_EVENT_IO_REQ]         = fsm_io_error,
                [VFIO_CCW_EVENT_INTERRUPT]      = fsm_irq,
+               [VFIO_CCW_EVENT_UPDATE_SUBCH]   = fsm_update_subch,
        },
        [VFIO_CCW_STATE_IDLE] = {
                [VFIO_CCW_EVENT_NOT_OPER]       = fsm_notoper,
                [VFIO_CCW_EVENT_IO_REQ]         = fsm_io_request,
                [VFIO_CCW_EVENT_INTERRUPT]      = fsm_irq,
+               [VFIO_CCW_EVENT_UPDATE_SUBCH]   = fsm_update_subch,
        },
        [VFIO_CCW_STATE_BOXED] = {
                [VFIO_CCW_EVENT_NOT_OPER]       = fsm_notoper,
                [VFIO_CCW_EVENT_IO_REQ]         = fsm_io_busy,
                [VFIO_CCW_EVENT_INTERRUPT]      = fsm_irq,
+               [VFIO_CCW_EVENT_UPDATE_SUBCH]   = fsm_update_subch,
        },
        [VFIO_CCW_STATE_BUSY] = {
                [VFIO_CCW_EVENT_NOT_OPER]       = fsm_notoper,
                [VFIO_CCW_EVENT_IO_REQ]         = fsm_io_busy,
                [VFIO_CCW_EVENT_INTERRUPT]      = fsm_irq,
+               [VFIO_CCW_EVENT_UPDATE_SUBCH]   = fsm_update_subch,
        },
  };
diff --git a/drivers/s390/cio/vfio_ccw_ops.c b/drivers/s390/cio/vfio_ccw_ops.c
index 41eeb57d68a3..9528fce2e7d9 100644
--- a/drivers/s390/cio/vfio_ccw_ops.c
+++ b/drivers/s390/cio/vfio_ccw_ops.c
@@ -13,6 +13,11 @@

  #include "vfio_ccw_private.h"

+#define VFIO_CCW_OFFSET_SHIFT   40
+#define VFIO_CCW_OFFSET_TO_INDEX(off)  (off >> VFIO_CCW_OFFSET_SHIFT)
+#define VFIO_CCW_INDEX_TO_OFFSET(index)        ((u64)(index) << 
VFIO_CCW_OFFSET_SHIFT)
+#define VFIO_CCW_OFFSET_MASK   (((u64)(1) << VFIO_CCW_OFFSET_SHIFT) - 1)
+
  static int vfio_ccw_mdev_reset(struct mdev_device *mdev)
  {
        struct vfio_ccw_private *private;
@@ -168,14 +173,31 @@ static ssize_t vfio_ccw_mdev_read(struct mdev_device 
*mdev,
                                  loff_t *ppos)
  {
        struct vfio_ccw_private *private;
-       struct ccw_io_region *region;
+       void *region;
+       u32 index;
+       loff_t pos;
+
+       index = VFIO_CCW_OFFSET_TO_INDEX(*ppos);
+       pos = (*ppos) & VFIO_CCW_OFFSET_MASK;
+       private = dev_get_drvdata(mdev_parent_dev(mdev));

-       if (*ppos + count > sizeof(*region))
+       switch (index) {
+       case VFIO_CCW_CONFIG_REGION_INDEX:
+               if (pos + count > sizeof(struct ccw_io_region))
+                       return -EINVAL;
+               region = &private->io_region;
+               break;
+       case VFIO_CCW_SCHIB_REGION_INDEX:
+               if (pos + count > sizeof(struct ccw_schib_region))
+                       return -EINVAL;
+               region = &private->schib_region;
+               vfio_ccw_fsm_event(private, VFIO_CCW_EVENT_UPDATE_SUBCH);
+               break;
+       default:
                return -EINVAL;
+       }

-       private = dev_get_drvdata(mdev_parent_dev(mdev));
-       region = &private->io_region;
-       if (copy_to_user(buf, (void *)region + *ppos, count))
+       if (copy_to_user(buf, region + pos, count))
                return -EFAULT;

        return count;
@@ -187,23 +209,35 @@ static ssize_t vfio_ccw_mdev_write(struct mdev_device 
*mdev,
                                   loff_t *ppos)
  {
        struct vfio_ccw_private *private;
-       struct ccw_io_region *region;
-
-       if (*ppos + count > sizeof(*region))
-               return -EINVAL;
+       u32 index;
+       loff_t pos;

+       index = VFIO_CCW_OFFSET_TO_INDEX(*ppos);
+       pos = (*ppos) & VFIO_CCW_OFFSET_MASK;
        private = dev_get_drvdata(mdev_parent_dev(mdev));
-       if (private->state != VFIO_CCW_STATE_IDLE)
-               return -EACCES;

-       region = &private->io_region;
-       if (copy_from_user((void *)region + *ppos, buf, count))
-               return -EFAULT;
-
-       vfio_ccw_fsm_event(private, VFIO_CCW_EVENT_IO_REQ);
-       if (region->ret_code != 0) {
-               private->state = VFIO_CCW_STATE_IDLE;
-               return region->ret_code;
+       switch (index) {
+       case VFIO_CCW_CONFIG_REGION_INDEX:
+       {
+               struct ccw_io_region *region;
+               if (pos + count > sizeof(*region))
+                       return -EINVAL;
+               if (private->state != VFIO_CCW_STATE_IDLE)
+                       return -EACCES;
+               region = &private->io_region;
+               if (copy_from_user((void *)region + *ppos, buf, count))
+                       return -EFAULT;
+               vfio_ccw_fsm_event(private, VFIO_CCW_EVENT_IO_REQ);
+               if (region->ret_code != 0) {
+                       private->state = VFIO_CCW_STATE_IDLE;
+                       return region->ret_code;
+               }
+               break;
+       }
+       case VFIO_CCW_SCHIB_REGION_INDEX:
+               return -EOPNOTSUPP;
+       default:
+               return -EINVAL;
        }

        return count;
@@ -224,11 +258,16 @@ static int vfio_ccw_mdev_get_region_info(struct 
vfio_region_info *info,
  {
        switch (info->index) {
        case VFIO_CCW_CONFIG_REGION_INDEX:
-               info->offset = 0;
+               info->offset = VFIO_CCW_INDEX_TO_OFFSET(info->index);
                info->size = sizeof(struct ccw_io_region);
                info->flags = VFIO_REGION_INFO_FLAG_READ
                              | VFIO_REGION_INFO_FLAG_WRITE;
                return 0;
+       case VFIO_CCW_SCHIB_REGION_INDEX:
+               info->offset = VFIO_CCW_INDEX_TO_OFFSET(info->index);
+               info->size = sizeof(struct ccw_schib_region);
+               info->flags = VFIO_REGION_INFO_FLAG_READ;
+               return 0;
        default:
                return -EINVAL;
        }
diff --git a/drivers/s390/cio/vfio_ccw_private.h 
b/drivers/s390/cio/vfio_ccw_private.h
index 78a66d96756b..460c8b90d834 100644
--- a/drivers/s390/cio/vfio_ccw_private.h
+++ b/drivers/s390/cio/vfio_ccw_private.h
@@ -28,6 +28,7 @@
   * @mdev: pointer to the mediated device
   * @nb: notifier for vfio events
   * @io_region: MMIO region to input/output I/O arguments/results
+ * @schib_region: MMIO region of subchannel information
   * @cp: channel program for the current I/O operation
   * @irb: irb info received from interrupt
   * @scsw: scsw info
@@ -42,6 +43,7 @@ struct vfio_ccw_private {
        struct mdev_device      *mdev;
        struct notifier_block   nb;
        struct ccw_io_region    io_region;
+       struct ccw_schib_region schib_region;

        struct channel_program  cp;
        struct irb              irb;


Hi,
I have a problem with these patches: you have 3 definitions for the subchannel status word: 
1: direct in the scsw entry of the vfio_ccw_private structure
2: indirect in the IRB structure irb
3: now in the scsw of the schib_region

How do you keep them all in sync?
The direct scsw in io region seems to only serve as a trigger used by userland, while the IRB in the io region and the SCHIB in the schib region are updated asynchronously, from hardware, one by polling (scsw in schib region), one by IRQ (scsw in irb in io region). 

I find this at least a source for obfuscation.

Regards,

Pierre


@@ -76,6 +78,7 @@ enum vfio_ccw_event {
        VFIO_CCW_EVENT_NOT_OPER,
        VFIO_CCW_EVENT_IO_REQ,
        VFIO_CCW_EVENT_INTERRUPT,
+       VFIO_CCW_EVENT_UPDATE_SUBCH,
        /* last element! */
        NR_VFIO_CCW_EVENTS
  };
diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
index e3301dbd27d4..c60244debf71 100644
--- a/include/uapi/linux/vfio.h
+++ b/include/uapi/linux/vfio.h
@@ -457,6 +457,7 @@ enum {

  enum {
        VFIO_CCW_CONFIG_REGION_INDEX,
+       VFIO_CCW_SCHIB_REGION_INDEX,
        VFIO_CCW_NUM_REGIONS
  };

diff --git a/include/uapi/linux/vfio_ccw.h b/include/uapi/linux/vfio_ccw.h
index 2ec5f367ff78..12508ef6e6fc 100644
--- a/include/uapi/linux/vfio_ccw.h
+++ b/include/uapi/linux/vfio_ccw.h
@@ -22,4 +22,10 @@ struct ccw_io_region {
        __u32   ret_code;
  } __packed;

+struct ccw_schib_region {
+       __u8    cc;
+#define SCHIB_AREA_SIZE 52
+       __u8    schib_area[SCHIB_AREA_SIZE];
+} __packed;
+
  #endif



--
Pierre Morel
Linux/KVM/QEMU in Böblingen - Germany
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