Documentation/x86: Rename resctrl_ui.rst and add two errata to the file

Intel Memory Bandwidth Monitoring (MBM) counters may report system
memory bandwidth incorrectly on some Intel processors. This is reported
in documented in erratum SKX99, erratum BDF102 and in the RDT reference
manual, see Documentation/x86/index.rst.

To work around the errata, MBM total and local readings are corrected
using a correction factor table.

Since the correction factor table is not publicly documented anywhere,
document the table and the errata in Documentation/x86/resctrl.rst for
future reference.

 [ bp: Move web links to the doc, massage. ]

Suggested-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Link: https://lkml.kernel.org/r/20201014004927.1839452-2-fenghua.yu@intel.com

2 files changed, 94 insertions, 1 deletions

diff --git a/Documentation/x86/index.rst b/Documentation/x86/index.rst
index b224d12c880b..9c6ebf355f81 100644
--- a/Documentation/x86/index.rst
+++ b/Documentation/x86/index.rst
@@ -27,7 +27,7 @@ x86-specific Documentation
    pti
    mds
    microcode
-   resctrl_ui
+   resctrl
    tsx_async_abort
    usb-legacy-support
    i386/index
diff --git a/Documentation/x86/resctrl_ui.rst b/Documentation/x86/resctrl.rst
index e59b7b93a9b4..71a531061e4e 100644
--- a/Documentation/x86/resctrl_ui.rst
+++ b/Documentation/x86/resctrl.rst
@@ -1209,3 +1209,96 @@ View the llc occupancy snapshot::
 
   # cat /sys/fs/resctrl/p1/mon_data/mon_L3_00/llc_occupancy
   11234000
+
+Intel RDT Errata
+================
+
+Intel MBM Counters May Report System Memory Bandwidth Incorrectly
+-----------------------------------------------------------------
+
+Errata SKX99 for Skylake server and BDF102 for Broadwell server.
+
+Problem: Intel Memory Bandwidth Monitoring (MBM) counters track metrics
+according to the assigned Resource Monitor ID (RMID) for that logical
+core. The IA32_QM_CTR register (MSR 0xC8E), used to report these
+metrics, may report incorrect system bandwidth for certain RMID values.
+
+Implication: Due to the errata, system memory bandwidth may not match
+what is reported.
+
+Workaround: MBM total and local readings are corrected according to the
+following correction factor table:
+
++---------------+---------------+---------------+-----------------+
+|core count	|rmid count	|rmid threshold	|correction factor|
++---------------+---------------+---------------+-----------------+
+|1		|8		|0		|1.000000	  |
++---------------+---------------+---------------+-----------------+
+|2		|16		|0		|1.000000	  |
++---------------+---------------+---------------+-----------------+
+|3		|24		|15		|0.969650	  |
++---------------+---------------+---------------+-----------------+
+|4		|32		|0		|1.000000	  |
++---------------+---------------+---------------+-----------------+
+|6		|48		|31		|0.969650	  |
++---------------+---------------+---------------+-----------------+
+|7		|56		|47		|1.142857	  |
++---------------+---------------+---------------+-----------------+
+|8		|64		|0		|1.000000	  |
++---------------+---------------+---------------+-----------------+
+|9		|72		|63		|1.185115	  |
++---------------+---------------+---------------+-----------------+
+|10		|80		|63		|1.066553	  |
++---------------+---------------+---------------+-----------------+
+|11		|88		|79		|1.454545	  |
++---------------+---------------+---------------+-----------------+
+|12		|96		|0		|1.000000	  |
++---------------+---------------+---------------+-----------------+
+|13		|104		|95		|1.230769	  |
++---------------+---------------+---------------+-----------------+
+|14		|112		|95		|1.142857	  |
++---------------+---------------+---------------+-----------------+
+|15		|120		|95		|1.066667	  |
++---------------+---------------+---------------+-----------------+
+|16		|128		|0		|1.000000	  |
++---------------+---------------+---------------+-----------------+
+|17		|136		|127		|1.254863	  |
++---------------+---------------+---------------+-----------------+
+|18		|144		|127		|1.185255	  |
++---------------+---------------+---------------+-----------------+
+|19		|152		|0		|1.000000	  |
++---------------+---------------+---------------+-----------------+
+|20		|160		|127		|1.066667	  |
++---------------+---------------+---------------+-----------------+
+|21		|168		|0		|1.000000	  |
++---------------+---------------+---------------+-----------------+
+|22		|176		|159		|1.454334	  |
++---------------+---------------+---------------+-----------------+
+|23		|184		|0		|1.000000	  |
++---------------+---------------+---------------+-----------------+
+|24		|192		|127		|0.969744	  |
++---------------+---------------+---------------+-----------------+
+|25		|200		|191		|1.280246	  |
++---------------+---------------+---------------+-----------------+
+|26		|208		|191		|1.230921	  |
++---------------+---------------+---------------+-----------------+
+|27		|216		|0		|1.000000	  |
++---------------+---------------+---------------+-----------------+
+|28		|224		|191		|1.143118	  |
++---------------+---------------+---------------+-----------------+
+
+If rmid > rmid threshold, MBM total and local values should be multiplied
+by the correction factor.
+
+See:
+
+1. Erratum SKX99 in Intel Xeon Processor Scalable Family Specification Update:
+http://web.archive.org/web/20200716124958/https://www.intel.com/content/www/us/en/processors/xeon/scalable/xeon-scalable-spec-update.html
+
+2. Erratum BDF102 in Intel Xeon E5-2600 v4 Processor Product Family Specification Update:
+http://web.archive.org/web/20191125200531/https://www.intel.com/content/dam/www/public/us/en/documents/specification-updates/xeon-e5-v4-spec-update.pdf
+
+3. The errata in Intel Resource Director Technology (Intel RDT) on 2nd Generation Intel Xeon Scalable Processors Reference Manual:
+https://software.intel.com/content/www/us/en/develop/articles/intel-resource-director-technology-rdt-reference-manual.html
+
+for further information.