[PATCH 0/3] Handle monitor trap flag during instruction emulation

[Oliver Upton <oupton@google.com>]

KVM already provides guests the ability to use the 'monitor trap flag'
VM-execution control. Support for this flag is provided by the fact that
KVM unconditionally forwards MTF VM-exits to the guest (if requested),
as KVM doesn't utilize MTF. While this provides support during hardware
instruction execution, it is insufficient for instruction emulation.

Should L0 emulate an instruction on the behalf of L2, L0 should also
synthesize an MTF VM-exit into L1, should control be set.

The first patch fixes the handling of #DB payloads for both Intel and
AMD. To support MTF, KVM must also populate the 'pending debug
exceptions' field, rather than directly manipulating the debug register
state. Additionally, the exception payload associated with #DB is said
to be compatible with the 'pending debug exceptions' field in VMX. This
does not map cleanly into an AMD DR6 register, requiring bit 12 (enabled
breakpoint on Intel, reserved MBZ on AMD) to be masked off.

The second patch implements MTF under instruction emulation by adding
vendor-specific hooks to kvm_skip_emulated_instruction(). Should any
non-debug exception be pending before this call, MTF will follow event
delivery. Otherwise, an MTF VM-exit may be synthesized directly into L1.

Third patch introduces tests to kvm-unit-tests. These tests path both
under virtualization and on bare-metal.

Oliver Upton (2):
  KVM: x86: Add vendor-specific #DB payload delivery
  KVM: x86: Emulate MTF when performing instruction emulation

 arch/x86/include/asm/kvm_host.h |  2 ++
 arch/x86/kvm/svm.c              | 25 +++++++++++++++++++++
 arch/x86/kvm/vmx/nested.c       |  2 +-
 arch/x86/kvm/vmx/nested.h       |  5 +++++
 arch/x86/kvm/vmx/vmx.c          | 39 ++++++++++++++++++++++++++++++++-
 arch/x86/kvm/x86.c              | 27 ++++++-----------------
 6 files changed, 78 insertions(+), 22 deletions(-)

-- 
2.25.0.rc1.283.g88dfdc4193-goog