[v2,00/10] KVM: Implement nested TSC scaling

Message

Ilias Stamatis May 12, 2021, 3:09 p.m. UTC

KVM currently supports hardware-assisted TSC scaling but only for L1;
the feature is not exposed to nested guests. This patch series adds
support for nested TSC scaling and allows both L1 and L2 to be scaled
with different scaling factors. That is achieved by "merging" the 01 and
02 values together.

Most of the logic in this series is implemented in common code (by doing
the necessary restructurings), however the patches add support for VMX
only. Adding support for SVM should be easy at this point and Maxim
Levitsky has volunteered to do this (thanks!).

Changelog:
v2:
  - Applied most (all?) of Maxim's feedback
  - Added a mul_s64_u64_shr function in math64.h
  - Added a separate kvm_scale_tsc_l1 function instead of passing an
    argument to kvm_scale_tsc
  - Implemented the 02 fields calculations in common code
  - Moved all of write_l1_tsc_offset's logic to common code
  - Added a check for whether the TSC is stable in patch 10
  - Used a random L1 factor and a negative offset in patch 10

Ilias Stamatis (10):
  math64.h: Add mul_s64_u64_shr()
  KVM: X86: Store L1's TSC scaling ratio in 'struct kvm_vcpu_arch'
  KVM: X86: Add kvm_scale_tsc_l1() and kvm_compute_tsc_offset_l1()
  KVM: VMX: Add a TSC multiplier field in VMCS12
  KVM: X86: Add functions for retrieving L2 TSC fields from common code
  KVM: X86: Add functions that calculate the 02 TSC offset and
    multiplier
  KVM: X86: Move write_l1_tsc_offset() logic to common code and rename
    it
  KVM: VMX: Set the TSC offset and multiplier on nested entry and exit
  KVM: VMX: Expose TSC scaling to L2
  KVM: selftests: x86: Add vmx_nested_tsc_scaling_test

 arch/x86/include/asm/kvm-x86-ops.h            |   4 +-
 arch/x86/include/asm/kvm_host.h               |  13 +-
 arch/x86/kvm/svm/svm.c                        |  29 ++-
 arch/x86/kvm/vmx/nested.c                     |  19 +-
 arch/x86/kvm/vmx/vmcs12.c                     |   1 +
 arch/x86/kvm/vmx/vmcs12.h                     |   4 +-
 arch/x86/kvm/vmx/vmx.c                        |  42 +--
 arch/x86/kvm/x86.c                            |  93 +++++--
 include/linux/math64.h                        |  19 ++
 tools/testing/selftests/kvm/.gitignore        |   1 +
 tools/testing/selftests/kvm/Makefile          |   1 +
 .../kvm/x86_64/vmx_nested_tsc_scaling_test.c  | 242 ++++++++++++++++++
 12 files changed, 409 insertions(+), 59 deletions(-)
 create mode 100644 tools/testing/selftests/kvm/x86_64/vmx_nested_tsc_scaling_test.c