[Qemu-devel] [PATCH] spapr_drc: don't allow 'empty' DRCs to be unisolated

[Michael Roth <mdroth@linux.vnet.ibm.com>]

Logical resources start with allocation-state:UNUSABLE /
isolation-state:ISOLATED. During hotplug, guests will transition
them to allocate-state:USABLE, and then to isolate-state:UNISOLATED.
The former transition does not seem to have any failure path for
cases where a DRC does not have any resources associated with it to
allocate for guest, but instead relies on the subsequent
isolation-state:UNISOLATED transition to indicate failure in this
situation.

Currently DRC code does not implement this logic, but instead
tries to indicate failure by refusing the allocation-state:USABLE
transition. Unfortunately, since that's not a documented failure
path, guests continue undeterred, causing undefined behavior in
QEMU and guest code.

Fix this by handling things as PAPR defines (13.7 and 13.7.3.1).

Cc: qemu-ppc@nongnu.org
Cc: David Gibson <david@gibson.dropbear.id.au>
Cc: Bharata B Rao <bharata@linux.vnet.ibm.com>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
---
 hw/ppc/spapr_drc.c         | 12 ++++++++++++
 include/hw/ppc/spapr_drc.h |  2 ++
 2 files changed, 14 insertions(+)

diff --git a/hw/ppc/spapr_drc.c b/hw/ppc/spapr_drc.c
index 9ce844a..c1f664f 100644
--- a/hw/ppc/spapr_drc.c
+++ b/hw/ppc/spapr_drc.c
@@ -66,6 +66,18 @@ static int set_isolation_state(sPAPRDRConnector *drc,
 
     DPRINTFN("drc: %x, set_isolation_state: %x", get_index(drc), state);
 
+    if (state == SPAPR_DR_ISOLATION_STATE_UNISOLATED) {
+        /* cannot unisolate a non-existant resource. this generally
+         * happens for logical resources where transitions from
+         * allocation-state:UNUSABLE to allocation-state:USABLE are
+         * unguarded, but instead rely on a subsequent
+         * isolation-state:UNISOLATED transition to indicate failure
+         */
+        if (!drc->dev) {
+            return -1;
+        }
+    }
+
     drc->isolation_state = state;
 
     if (drc->isolation_state == SPAPR_DR_ISOLATION_STATE_ISOLATED) {
diff --git a/include/hw/ppc/spapr_drc.h b/include/hw/ppc/spapr_drc.h
index 28ffeae..3fbe9ea 100644
--- a/include/hw/ppc/spapr_drc.h
+++ b/include/hw/ppc/spapr_drc.h
@@ -109,6 +109,7 @@ typedef enum {
  * unusable: device not currently available to OS
  * exchange: (currently unused)
  * recover: (currently unused)
+ * no_sensor: for logical DR only, returned when no resource available
  */
 typedef enum {
     SPAPR_DR_ENTITY_SENSE_EMPTY     = 0,
@@ -116,6 +117,7 @@ typedef enum {
     SPAPR_DR_ENTITY_SENSE_UNUSABLE  = 2,
     SPAPR_DR_ENTITY_SENSE_EXCHANGE  = 3,
     SPAPR_DR_ENTITY_SENSE_RECOVER   = 4,
+    SPAPR_DR_ENTITY_SENSE_NO_SENSOR = -3,
 } sPAPRDREntitySense;
 
 typedef enum {
-- 
1.9.1