Use per-core mutex for XSCOM for P8 errata.

    See HW822317.  The HMER register in P8 is not implemented to
    handle multi-threaded XSCOM properly, so we need to move the
    XSCOM mutex from per-thread to per-core.  Also, there is an
    issue where the 'done' bit can come on 1 cycle before the error
    indicators, so need to potentially read the HMER a second time.

Change-Id: I495031a6e425fe7d5c6ffef8dda1e7a71caac9f2
CQ: SW250902
Backport: release-fips810
Reviewed-on: http://gfw160.aus.stglabs.ibm.com:8080/gerrit/9929
Reviewed-by: Michael Baiocchi <baiocchi@us.ibm.com>
Reviewed-by: A. Patrick Williams III <iawillia@us.ibm.com>
Tested-by: Jenkins Server

2 files changed, 38 insertions, 2 deletions

diff --git a/src/kernel/cpumgr.C b/src/kernel/cpumgr.C
index 624751b5c..ac0e09dff 100644
--- a/src/kernel/cpumgr.C
+++ b/src/kernel/cpumgr.C
@@ -5,7 +5,7 @@
 /*                                                                        */
 /* IBM CONFIDENTIAL                                                       */
 /*                                                                        */
-/* COPYRIGHT International Business Machines Corp. 2010,2013              */
+/* COPYRIGHT International Business Machines Corp. 2010,2014              */
 /*                                                                        */
 /* p1                                                                     */
 /*                                                                        */
@@ -42,6 +42,7 @@
 #include <kernel/terminate.H>
 #include <kernel/hbterminatetypes.H>
 #include <kernel/kernel_reasoncodes.H>
+#include <kernel/cpuid.H>
 
 cpu_t** CpuManager::cv_cpus[KERNEL_MAX_SUPPORTED_NODES];
 bool CpuManager::cv_shutdown_requested = false;
@@ -214,7 +215,34 @@ void CpuManager::startCPU(ssize_t i)
             reinterpret_cast<uintptr_t>(cpu->kernel_stack_bottom) +
             kernel_page_offset);
 
-        cpu->xscom_mutex = (mutex_t)MUTEX_INITIALIZER;
+        cpu->xscom_mutex = NULL;
+
+        // xscom workaround for HW822317 : Power8 Errata.
+        //     Need to make the xscom mutex a per-core mutex to prevent
+        //     multi-threaded access to the HMER.
+        if ((CpuID::getCpuType() == CORE_POWER8_MURANO) ||
+            (CpuID::getCpuType() == CORE_POWER8_VENICE))
+        {
+            const size_t num_threads = getThreadCount();
+            size_t cpu_idx = (cpuId / num_threads) * num_threads;
+
+            for(size_t i = 0; i < getThreadCount(); ++i)
+            {
+                if ((NULL != cv_cpus[nodeId][cpu_idx + i]) &&
+                    (NULL != cv_cpus[nodeId][cpu_idx + i]->xscom_mutex))
+                {
+                    cpu->xscom_mutex =
+                        cv_cpus[nodeId][cpu_idx + i]->xscom_mutex;
+                    break;
+                }
+            }
+        }
+
+        if (NULL == cpu->xscom_mutex)
+        {
+            cpu->xscom_mutex = new mutex_t;
+            mutex_init(cpu->xscom_mutex);
+        }
 
         // Create idle task.
         cpu->idle_task = TaskManager::createIdleTask();
diff --git a/src/kernel/start.S b/src/kernel/start.S
index 790281305..b6f09d40e 100644
--- a/src/kernel/start.S
+++ b/src/kernel/start.S
@@ -707,6 +707,14 @@ system_call_fast_path:
         ;// Compare was already done in system call path.
     bne cr0, 2f
     mfspr r3, HMER
+        ;// Do XSCOM workaround for Errata HW822317.
+        ;// If the done bit (10) is on in HMER, it could take another cycle
+        ;// for any error status to show up.  Perform another HMER read.
+    rldicr. r0, r3, 10, 0
+    beq cr0, 1f                 ;// Done bit not set, jump to exit.
+    mfspr r0, HMER              ;// Read HMER again and OR results.
+    or r3, r3, r0
+        ;// --- end workaround HW822317
     b 1f                        ;// Jump to exit point.
         ;// Check if this is HMER write (0x801).
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