skiboot 6.0.4 release notes

Signed-off-by: Stewart Smith <stewart@linux.ibm.com>

doc/release-notes/skiboot-6.0.4.rst

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+.. _skiboot-6.0.4:
+
+=============
+skiboot-6.0.4
+=============
+
+skiboot 6.0.4 was released on Monday May 28th, 2018. It replaces
+:ref:`skiboot-6.0.3` as the current stable release in the 6.0.x series.
+
+It is recommended that 6.0.4 be used instead of any previous 6.0.x version.
+
+Over :ref:`skiboot-6.0.3`, we have two bug fixes: one helps with performance
+(especially in HPC environments), and one is an opal-prd fix.
+
+Changes are:
+
+- SLW: Remove stop1_lite and stop2_lite
+
+  stop1_lite has been removed since it adds no additional benefit
+  over stop0_lite. stop2_lite has been removed since currently it adds
+  minimal benefit over stop2. However, the benefit is eclipsed by the time
+  required to ungate the clocks
+
+  Moreover, Lite states don't give up the SMT resources, can potentially
+  have a performance impact on sibling threads.
+
+  Since current OSs (Linux) aren't smart enough to make good decisions
+  with these stop states, we're (temporarly) removing them from what
+  we expose to the OS, the idea being to bring them back in a new
+  DT representation so that only an OS that knows what to do will
+  do things with them.
+- opal-prd: Do not error out on first failure for soft/hard offline.
+
+  The memory errors (CEs and UEs) that are detected as part of background
+  memory scrubbing are reported by PRD asynchronously to opal-prd along with
+  affected memory ranges. hservice_memory_error() converts these ranges into
+  page granularity before hooking up them to soft/hard offline-ing
+  infrastructure.
+
+  But the current implementation of hservice_memory_error() does not hookup
+  all the pages to soft/hard offline-ing if any of the page offline action
+  fails. e.g hard offline can fail for:
+
+  - Pages that are not part of buddy managed pool.
+  - Pages that are reserved by kernel using memblock_reserved()
+  - Pages that are in use by kernel.
+
+  But for the pages that are in use by user space application, the hard
+  offline marks the page as hwpoison, sends SIGBUS signal to kill the
+  affected application as recovery action and returns success.
+
+  Hence, It is possible that some of the pages in that memory range are in
+  use by application or free. By stopping on first error we loose the
+  opportunity to hwpoison the subsequent pages which may be free or in use by
+  application. This patch fixes this issue.