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

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Date:   Mon, 24 May 2021 17:37:25 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Ilias Stamatis <ilstam@...zon.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     mlevitsk@...hat.com, seanjc@...gle.com, vkuznets@...hat.com,
        wanpengli@...cent.com, jmattson@...gle.com, joro@...tes.org,
        zamsden@...il.com, mtosatti@...hat.com, dwmw@...zon.co.uk
Subject: Re: [PATCH v3 00/12] KVM: Implement nested TSC scaling

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