v4 more sampling fun 0

From: mark gross <[email protected]>
Subject: [PATCH 0/3] v4 more sampling fun

This version of the Special Register Buffer Data Sampling has been updated to address feedback gotten. Including:
* changes x86_cpu_id as a prerequisite patch similar to the initial version posted a few weeks ago.
* simplified the affected processor table
* renamed the VULNWL* macros to VULNHW*
* added an ABI note introducing the sysfs addition
* assorted clean ups and some additional inline commentary.

---

Special Register Buffer Data Sampling is a sampling type of vulnerability that leaks data across cores sharing the HW-RNG for vulnerable processors.

This leak is fixed by a microcode update and is enabled by default.

This new microcode serializes processor access during execution of RDRAND or RDSEED. It ensures that the shared buffer is overwritten before it is released for reuse.

The mitigation impacts the throughput of the RDRAND and RDSEED instructions and latency of RT processing running on the socket while executing RDRAND or RDSEED. The micro benchmark of calling RDRAND many times shows a slowdown.

This patch set enables kernel command line control of this mitigation and exports vulnerability and mitigation status.
This patch set includes 3 patches:
* The first patch extends match.c and mod-devicetable.h to include steppings.
* The second patch enables the command line control of the mitigation as well as the sysfs export of vulnerability status.
* The third patch has the Documentation/admin-guide/hw-vuln documentation for this issue and the control over the mitigation.

The microcode defaults to enabling the mitigation.

mark gross (3):
x86/cpu: Add stepping field to x86_cpu_id structure x86/speculation: Special Register Buffer Data Sampling (SRBDS)
mitigation control.
x86/speculation: SRBDS vulnerability and mitigation documentation

 .../ABI/testing/sysfs-devices-system-cpu      |   1 +
 Documentation/admin-guide/hw-vuln/index.rst   |   2 +
 .../special-register-buffer-data-sampling.rst | 150 ++++++++++++++++++
 .../admin-guide/kernel-parameters.txt         |  11 ++
 arch/x86/include/asm/cpufeatures.h            |   2 +
 arch/x86/include/asm/msr-index.h              |   4 +
 arch/x86/kernel/cpu/bugs.c                    | 112 +++++++++++++
 arch/x86/kernel/cpu/common.c                  | 128 +++++++++------
 arch/x86/kernel/cpu/cpu.h                     |  13 ++
 arch/x86/kernel/cpu/intel.c                   |   2 +
 arch/x86/kernel/cpu/match.c                   |   6 +-
 drivers/base/cpu.c                            |   8 +
 include/linux/mod_devicetable.h               |   2 +
 13 files changed, 391 insertions(+), 50 deletions(-)
 create mode 100644 Documentation/admin-guide/hw-vuln/special-register-buffer-data-sampling.rst

2.17.1