Re: [PATCH v3 00/12] KVM: Implement nested TSC scaling

Paolo Bonzini
2021-05-24T15:42:26Z

On 21/05/21 12:24, Ilias Stamatis wrote:
> 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:
> v3:
> - Applied Sean's feedback
> - Refactored patches 7 to 10
>
> v2:
> - Applied 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 (12):
> math64.h: Add mul_s64_u64_shr()
> KVM: X86: Store L1's TSC scaling ratio in 'struct kvm_vcpu_arch'
> KVM: X86: Rename kvm_compute_tsc_offset() to
> kvm_compute_tsc_offset_l1()
> KVM: X86: Add a ratio parameter to kvm_scale_tsc()
> 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 L2's TSC offset and multiplier
> KVM: X86: Move write_l1_tsc_offset() logic to common code and rename
> it
> KVM: VMX: Remove vmx->current_tsc_ratio and decache_tsc_multiplier()
> 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 | 14 +-
> arch/x86/kvm/svm/svm.c | 29 ++-
> arch/x86/kvm/vmx/nested.c | 33 ++-
> arch/x86/kvm/vmx/vmcs12.c | 1 +
> arch/x86/kvm/vmx/vmcs12.h | 4 +-
> arch/x86/kvm/vmx/vmx.c | 49 ++--
> arch/x86/kvm/vmx/vmx.h | 11 +-
> arch/x86/kvm/x86.c | 91 +++++--
> 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 ++++++++++++++++++
> 13 files changed, 417 insertions(+), 82 deletions(-)
> create mode 100644 tools/testing/selftests/kvm/x86_64/vmx_nested_tsc_scaling_test.c
>
> --
> 2.17.1
>

Queued, thanks.

The new kvm_x86_ops should go in kvm_x86_ops.nested, but those are not
yet static_calls so we can leave that for later.

Paolo