MDD v1.3.1

Since v3:
- Fixed the bug where IBRS was enabled when going in the kernel.
- Untangled two patches.

Couple of things:

- 'Memory disambiguation disable mitigation is enabled' sounds horrible. I ended up picking up for sysfs 'md' and for x86 speaking about 'mdd' and putting the parameters around the 'disable' part.

- No AMD SVM support as I don't know the bits.

- The last two patches are crap. I should have used the latest one from Tim Chen, but it may be an academic point as folks may just decide that having this memory disambiguation being enabled/disabled when switching between kernel and userspace is not worth it.

- It works nicely.

 Documentation/admin-guide/kernel-parameters.txt |  11 +++
 arch/x86/entry/entry_64.S                       |  14 ++-
 arch/x86/entry/entry_64_compat.S                |   7 ++
 arch/x86/include/asm/cpufeatures.h              |   3 +
 arch/x86/include/asm/msr-index.h                |   1 +
 arch/x86/include/asm/nospec-branch.h            | 103 +++++++++++++++++++-
 arch/x86/kernel/cpu/bugs.c                      | 119 ++++++++++++++++++++++++
 arch/x86/kernel/cpu/common.c                    |  20 ++++
 arch/x86/kernel/cpu/intel.c                     |   1 +
 arch/x86/kvm/cpuid.c                            |   2 +-
 arch/x86/kvm/vmx.c                              |  14 +--
 drivers/base/cpu.c                              |   8 ++
 include/linux/cpu.h                             |   2 +
 13 files changed, 293 insertions(+), 12 deletions(-)

Konrad Rzeszutek Wilk (7):
x86/mdd: Expose the /sys/../md and BUG_MD
x86/mdd: Provide boot parameters to select which MD mitigation to use. x86/mdd: If MD is disabled at bootup, then set the SPEC_CTRL MSR. x86/mdd/firmware calls: Save/Restore the MDD bit when using SPEC_CTRL x86/mdd/KVM: Support the combination of guest IBRS and ours. x86/mdd: Add [ENABLE|DISABLE]_SPEC_CTRL_[|CLOBBER] and variants. x86/mdd: Add SPEC_CTRL macros on system call/interrupts/exceptions/etc