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

[Like Xu <like.xu@linux.intel.com>]

Hi Paolo,

Do you have any comments on the patches 06 - 11 ?

Thanks,
Like Xu

On 2021/4/6 11:19, Xu, Like wrote:
> 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(-)
>>
>