mbox series

[v6,00/12] Introduce Architectural LBR for vPMU

Message ID 1626425406-18582-1-git-send-email-weijiang.yang@intel.com (mailing list archive)
Headers show
Series Introduce Architectural LBR for vPMU | expand

Message

Yang, Weijiang July 16, 2021, 8:49 a.m. UTC 
The Architectural Last Branch Records (LBRs) is published in the 319433-040
release of Intel Architecture Instruction Set Extensions and Future Features
Programming Reference[0].

The main advantages of Arch LBR 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.

From end user's point of view, the usage of Arch LBR is the same as
the Legacy LBR that has been merged in the mainline.

Note, there's one limitations for current guest Arch LBR implementation:
Guest can only use the same LBR record depth as host, this is due to
the special behavior of MSR_ARCH_LBR_DEPTH: a) On write to the MSR,
it'll reset all Arch LBR recording MSRs to 0s. b) XRSTORS will reset all
recording MSRs to 0s if the saved depth mismatches MSR_ARCH_LBR_DEPTH.

But this limitation won't impact guest perf tool usage.

Regarding the MSR_ARCH_LBR_CTL handling in SMM and #DB, pending details
inquiry to spec. owner, will enclose related patches if necessary.

[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/


Previous version:
v5: https://lkml.kernel.org/kvm/1625825111-6604-1-git-send-email-weijiang.yang@intel.com/

Changes in v6:
1. Removed host MSR_ARCH_LBR_CTL save/restore patch as it won't benefit host Arch LBR profiling. <Jim M.>
2. Removed arch_lbr_reset flag as it'll make things complicated/broken. <Jim M.>
3. Fixed a few issues in setting Arch LBR MSRs. <Jim M.>
4. Explicitly mask the Arch LBR depth in guest CPUID so that guest only sees the supported value.
5. Other minor fixes per Jim's review feedback.

Like Xu (6):
  perf/x86/intel: Fix the comment about guest LBR support on KVM
  perf/x86/lbr: Simplify the exposure check for the LBR_INFO registers
  KVM: vmx/pmu: Emulate MSR_ARCH_LBR_DEPTH for guest Arch LBR
  KVM: vmx/pmu: Emulate MSR_ARCH_LBR_CTL for guest Arch LBR
  KVM: x86: Refine the matching and clearing logic for supported_xss
  KVM: x86: Add XSAVE Support for Architectural LBR

Sean Christopherson (1):
  KVM: x86: Report XSS as an MSR to be saved if there are supported
    features

Yang Weijiang (5):
  KVM: x86: Add arch LBR MSRs to msrs_to_save_all list
  KVM: x86/pmu: Refactor code to support guest Arch LBR
  KVM: x86: Refresh CPUID on writes to MSR_IA32_XSS
  KVM: x86/vmx: Check Arch LBR config  when return perf capabilities
  KVM: x86/cpuid: Advise Arch LBR feature in CPUID

 arch/x86/events/intel/core.c     |   3 +-
 arch/x86/events/intel/lbr.c      |   6 +-
 arch/x86/include/asm/kvm_host.h  |   1 +
 arch/x86/include/asm/msr-index.h |   1 +
 arch/x86/include/asm/vmx.h       |   4 ++
 arch/x86/kvm/cpuid.c             |  54 ++++++++++++--
 arch/x86/kvm/vmx/capabilities.h  |  25 ++++---
 arch/x86/kvm/vmx/pmu_intel.c     | 120 +++++++++++++++++++++++++++----
 arch/x86/kvm/vmx/vmx.c           |  27 +++++--
 arch/x86/kvm/x86.c               |  24 ++++++-
 10 files changed, 226 insertions(+), 39 deletions(-)