kvm/split_lock: Add feature split lock detection support in kvm

This patchset aims to add the virtualization of split lock detection
for guest, while containing the fix of X86_FEATURE_SPLIT_LOCK_DETECT that
KVM needs to ensure the existence of feature through this flag.

Whether or not we advertise split lock detection to guest, we have to make
a choice between not burning the old guest and preventing DoS attack from
guest since we cannot identify whether a guest is malicious.

Since sld_warn mode allows userspace applications to do split lock, we
extend the same policy to guest that regards guest as user space application
and use handle_user_split_lock() to handle unexpected #AC caused by split
lock.

To prevent DoS attack from either host or guest, we must use
split_lock_detec=fatal in host.

BTW, Andy,

We will talk to Intel hardware architect about the suggestion of MSR_TEST_CTRL
sticky/lock bit[1] if you think it's OK.

[1]: https://lore.kernel.org/kvm/20200204060353.GB31665@linux....

Xiaoyao Li (8):
  x86/split_lock: Export handle_user_split_lock()
  x86/split_lock: Ensure X86_FEATURE_SPLIT_LOCK_DETECT means the
    existence of feature
  x86/split_lock: Cache the value of MSR_TEST_CTRL in percpu data
  x86/split_lock: Add and export split_lock_detect_enabled() and
    split_lock_detect_fatal()
  kvm: x86: Emulate split-lock access as a write
  kvm: vmx: Extend VMX's #AC interceptor to handle split lock #AC
    happens in guest
  kvm: x86: Emulate MSR IA32_CORE_CAPABILITIES
  x86: vmx: virtualize split lock detection

 arch/x86/include/asm/cpu.h      | 12 ++++-
 arch/x86/include/asm/kvm_host.h |  1 +
 arch/x86/kernel/cpu/intel.c     | 82 +++++++++++++++++++++----------
 arch/x86/kernel/traps.c         |  2 +-
 arch/x86/kvm/cpuid.c            |  5 +-
 arch/x86/kvm/vmx/vmx.c          | 86 +++++++++++++++++++++++++++++++--
 arch/x86/kvm/vmx/vmx.h          |  1 +
 arch/x86/kvm/x86.c              | 41 +++++++++++++++-
 8 files changed, 194 insertions(+), 36 deletions(-)

-- 
2.23.0