linux-kernel - Re: [PATCH v4 00/11] KVM: x86/pmu: Guest Architectural LBR Enabling

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Date:   Tue, 6 Apr 2021 11:19:39 +0800
From:   "Xu, Like" <like.xu@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        x86@...nel.org, wei.w.wang@...el.com, linux-kernel@...r.kernel.org,
        Like Xu <like.xu@...ux.intel.com>
Subject: Re: [PATCH v4 00/11] KVM: x86/pmu: Guest Architectural LBR Enabling

Hi all, do we have any comments on this patch set?

On 2021/3/14 23:52, Like Xu wrote:
> Hi geniuses,
>
> Please help review the new version of Arch LBR enabling patch set.
>
> The Architectural Last Branch Records (LBRs) is publiced
> in the 319433-040 release of Intel Architecture Instruction
> Set Extensions and Future Features Programming Reference[0].
>
> The main advantages for the Arch LBR users are [1]:
> - Faster context switching due to XSAVES support and faster reset of
>    LBR MSRs via the new DEPTH MSR
> - Faster LBR read for a non-PEBS event due to XSAVES support, which
>    lowers the overhead of the NMI handler.
> - Linux kernel can support the LBR features without knowing the model
>    number of the current CPU.
>
> It's based on the kvm/queue tree plus two commits from kvm/intel tree:
> - 'fea4ab260645 ("KVM: x86: Refresh CPUID on writes to MSR_IA32_XSS")'
> - '0ccd14126cb2 ("KVM: x86: Report XSS as an MSR to be saved if there are supported features")'
>
> Please check more details in each commit and feel free to comment.
>
> [0] https://software.intel.com/content/www/us/en/develop/download/
> intel-architecture-instruction-set-extensions-and-future-features-programming-reference.html
> [1] https://lore.kernel.org/lkml/1593780569-62993-1-git-send-email-kan.liang@linux.intel.com/
>
> ---
> v3->v4 Changelog:
> - Add one more host patch to reuse ARCH_LBR_CTL_MASK;
> - Add reserve_lbr_buffers() instead of using GFP_ATOMIC;
> - Fia a bug in the arch_lbr_depth_is_valid();
> - Add LBR_CTL_EN to unify DEBUGCTLMSR_LBR and ARCH_LBR_CTL_LBREN;
> - Add vmx->host_lbrctlmsr to save/restore host values;
> - Add KVM_SUPPORTED_XSS to refactoring supported_xss;
> - Clear Arch_LBR ans its XSS bit if it's not supported;
> - Add negative testing to the related kvm-unit-tests;
> - Refine code and commit messages;
>
> Previous:
> https://lore.kernel.org/kvm/20210303135756.1546253-1-like.xu@linux.intel.com/
>
> Like Xu (11):
>    perf/x86/intel: Fix the comment about guest LBR support on KVM
>    perf/x86/lbr: Simplify the exposure check for the LBR_INFO registers
>    perf/x86/lbr: Skip checking for the existence of LBR_TOS for Arch LBR
>    perf/x86/lbr: Move cpuc->lbr_xsave allocation out of sleeping region
>    perf/x86: Move ARCH_LBR_CTL_MASK definition to include/asm/msr-index.h
>    KVM: vmx/pmu: Add MSR_ARCH_LBR_DEPTH emulation for Arch LBR
>    KVM: vmx/pmu: Add MSR_ARCH_LBR_CTL emulation for Arch LBR
>    KVM: vmx/pmu: Add Arch LBR emulation and its VMCS field
>    KVM: x86: Expose Architectural LBR CPUID leaf
>    KVM: x86: Refine the matching and clearing logic for supported_xss
>    KVM: x86: Add XSAVE Support for Architectural LBRs
>
>   arch/x86/events/core.c           |   8 ++-
>   arch/x86/events/intel/bts.c      |   2 +-
>   arch/x86/events/intel/core.c     |   6 +-
>   arch/x86/events/intel/lbr.c      |  28 +++++----
>   arch/x86/events/perf_event.h     |   8 ++-
>   arch/x86/include/asm/msr-index.h |   1 +
>   arch/x86/include/asm/vmx.h       |   4 ++
>   arch/x86/kvm/cpuid.c             |  25 +++++++-
>   arch/x86/kvm/vmx/capabilities.h  |  25 +++++---
>   arch/x86/kvm/vmx/pmu_intel.c     | 103 ++++++++++++++++++++++++++++---
>   arch/x86/kvm/vmx/vmx.c           |  50 +++++++++++++--
>   arch/x86/kvm/vmx/vmx.h           |   4 ++
>   arch/x86/kvm/x86.c               |   6 +-
>   13 files changed, 227 insertions(+), 43 deletions(-)
>