[Qemu-devel] [PATCH for-2.6] spapr_drc: enable immediate detach for unsignalled devices

[Michael Roth]

Currently spapr doesn't support "aborting" hotplug of PCI
devices by allowing device_del to immediately remove the
device if we haven't signalled the presence of the device
to the guest.

In the past this wasn't an issue, since we always immediately
signalled device attach and simply relied on full guest-aware
add->remove path for device removal. However, as of 788d259,
we now defer signalling for PCI functions until function 0
is attached, so now we need to deal with these "abort" operations
for cases where a user hotplugs a non-0 function, then opts to
remove it prior hotplugging function 0. Currently they'd have to
reboot before the unplug completed. PCIe multifunction hotplug
does not have this requirement however, so from a management
implementation perspective it would be good to address this within
the same release as 788d259.

We accomplish this by simply adding a 'signalled' flag to track
whether a device hotplug event has been sent to the guest. If it
hasn't, we allow immediate removal under the assumption that the
guest will not be using the device. Devices present at boot/reset
time are also assumed to be 'signalled'.

For CPU/memory/etc, signalling will still happen immediately
as part of device_add, so only PCI functions should be affected.

Cc: address@hidden
Cc: address@hidden
Cc: address@hidden
Cc: address@hidden
Signed-off-by: Michael Roth <address@hidden>
---
 hw/ppc/spapr_drc.c         | 34 ++++++++++++++++++++++++++++++++++
 hw/ppc/spapr_events.c      | 11 +++++++++++
 include/hw/ppc/spapr_drc.h |  2 ++
 3 files changed, 47 insertions(+)

diff --git a/hw/ppc/spapr_drc.c b/hw/ppc/spapr_drc.c
index ef063c0..5568e44 100644
--- a/hw/ppc/spapr_drc.c
+++ b/hw/ppc/spapr_drc.c
@@ -173,6 +173,12 @@ static void set_configured(sPAPRDRConnector *drc)
     drc->configured = true;
 }
 
+/* has the guest been notified of device attachment? */
+static void set_signalled(sPAPRDRConnector *drc)
+{
+    drc->signalled = true;
+}
+
 /*
  * dr-entity-sense sensor value
  * returned via get-sensor-state RTAS calls
@@ -355,6 +361,7 @@ static void attach(sPAPRDRConnector *drc, DeviceState *d, 
void *fdt,
     drc->fdt = fdt;
     drc->fdt_start_offset = fdt_start_offset;
     drc->configured = coldplug;
+    drc->signalled = coldplug;
 
     object_property_add_link(OBJECT(drc), "device",
                              object_get_typename(OBJECT(drc->dev)),
@@ -371,6 +378,26 @@ static void detach(sPAPRDRConnector *drc, DeviceState *d,
     drc->detach_cb = detach_cb;
     drc->detach_cb_opaque = detach_cb_opaque;
 
+    /* if we've signalled device presence to the guest, or if the guest
+     * has gone ahead and configured the device (via manually-executed
+     * device add via drmgr in guest, namely), we need to wait
+     * for the guest to quiesce the device before completing detach.
+     * Otherwise, we can assume the guest hasn't seen it and complete the
+     * detach immediately. Note that there is a small race window
+     * just before, or during, configuration, which is this context
+     * refers mainly to fetching the device tree via RTAS.
+     * During this window the device access will be arbitrated by
+     * associated DRC, which will simply fail the RTAS calls as invalid.
+     * This is recoverable within guest and current implementations of
+     * drmgr should be able to cope.
+     */
+    if (!drc->signalled && !drc->configured) {
+        /* if the guest hasn't seen the device we can't rely on it to
+         * set it back to an isolated state via RTAS, so do it here manually
+         */
+        drc->isolation_state = SPAPR_DR_ISOLATION_STATE_ISOLATED;
+    }
+
     if (drc->isolation_state != SPAPR_DR_ISOLATION_STATE_ISOLATED) {
         DPRINTFN("awaiting transition to isolated state before removal");
         drc->awaiting_release = true;
@@ -409,6 +436,7 @@ static void reset(DeviceState *d)
 {
     sPAPRDRConnector *drc = SPAPR_DR_CONNECTOR(d);
     sPAPRDRConnectorClass *drck = SPAPR_DR_CONNECTOR_GET_CLASS(drc);
+    sPAPRDREntitySense state;
 
     DPRINTFN("drc reset: %x", drck->get_index(drc));
     /* immediately upon reset we can safely assume DRCs whose devices
@@ -436,6 +464,11 @@ static void reset(DeviceState *d)
             drck->set_allocation_state(drc, 
SPAPR_DR_ALLOCATION_STATE_UNUSABLE);
         }
     }
+
+    drck->entity_sense(drc, &state);
+    if (state == SPAPR_DR_ENTITY_SENSE_PRESENT) {
+        drck->set_signalled(drc);
+    }
 }
 
 static void realize(DeviceState *d, Error **errp)
@@ -594,6 +627,7 @@ static void spapr_dr_connector_class_init(ObjectClass *k, 
void *data)
     drck->attach = attach;
     drck->detach = detach;
     drck->release_pending = release_pending;
+    drck->set_signalled = set_signalled;
     /*
      * Reason: it crashes FIXME find and document the real reason
      */
diff --git a/hw/ppc/spapr_events.c b/hw/ppc/spapr_events.c
index 39f4682..be8de63 100644
--- a/hw/ppc/spapr_events.c
+++ b/hw/ppc/spapr_events.c
@@ -387,6 +387,13 @@ static void spapr_powerdown_req(Notifier *n, void *opaque)
     qemu_irq_pulse(xics_get_qirq(spapr->icp, spapr->check_exception_irq));
 }
 
+static void spapr_hotplug_set_signalled(uint32_t drc_index)
+{
+    sPAPRDRConnector *drc = spapr_dr_connector_by_index(drc_index);
+    sPAPRDRConnectorClass *drck = SPAPR_DR_CONNECTOR_GET_CLASS(drc);
+    drck->set_signalled(drc);
+}
+
 static void spapr_hotplug_req_event(uint8_t hp_id, uint8_t hp_action,
                                     sPAPRDRConnectorType drc_type,
                                     uint32_t drc)
@@ -453,6 +460,10 @@ static void spapr_hotplug_req_event(uint8_t hp_id, uint8_t 
hp_action,
 
     rtas_event_log_queue(RTAS_LOG_TYPE_HOTPLUG, new_hp, true);
 
+    if (hp->hotplug_action == RTAS_LOG_V6_HP_ACTION_ADD) {
+        spapr_hotplug_set_signalled(drc);
+    }
+
     qemu_irq_pulse(xics_get_qirq(spapr->icp, spapr->check_exception_irq));
 }
 
diff --git a/include/hw/ppc/spapr_drc.h b/include/hw/ppc/spapr_drc.h
index 7e56347..fa21ba0 100644
--- a/include/hw/ppc/spapr_drc.h
+++ b/include/hw/ppc/spapr_drc.h
@@ -151,6 +151,7 @@ typedef struct sPAPRDRConnector {
     bool configured;
 
     bool awaiting_release;
+    bool signalled;
 
     /* device pointer, via link property */
     DeviceState *dev;
@@ -188,6 +189,7 @@ typedef struct sPAPRDRConnectorClass {
                    spapr_drc_detach_cb *detach_cb,
                    void *detach_cb_opaque, Error **errp);
     bool (*release_pending)(sPAPRDRConnector *drc);
+    void (*set_signalled)(sPAPRDRConnector *drc);
 } sPAPRDRConnectorClass;
 
 sPAPRDRConnector *spapr_dr_connector_new(Object *owner,
-- 
1.9.1