[PATCH 0/6] Guest Architectural LBR Enabling

Like Xu
2020-07-31T07:46:10Z

Hi All (especially developers who use perf in guest),

Please help review the ssuccessor pacthes to enable Arch LBR on KVM.
(The prerequisite v13 LBR patchset [2] seems more eager to get
the attention of reviewers and maintainer).

LBR (Last Branch Records) enables recording of software path history
by logging taken branches and other control flows within architectural
registers. Intel CPUs have had model-specific LBRs for quite some time
but this evolves them into an architectural feature now.

The Architectural Last Branch Records (LBRS) is already 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. (For a PEBS event, the LBR
information is recorded in the PEBS records. There is no impact on
the PEBS event.)
- Linux kernel can support the LBR features without knowing the model
number of the current CPU.

The Kernel 5.9 will enable Arch LBR on the host based on
tip/perf/core, so this patchset happens to enable it on KVM as well.

Before 'git am' this patchset, you may need merge the latest
tip/perf/core branch and the legacy LBR enabling patches
[PATCH v13 00/10] Guest Last Branch Recording Enabling [2].
or just wait for the above pacthes to be merged upstream.

[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/
[2] https://lore.kernel.org/kvm/20200726153229.27149-1-like.xu@linux.intel.com/

Please check more details in each commit and feel free to comment.

Like Xu (6):
KVM: vmx/pmu: Add VMCS field check before exposing LBR_FMT
perf/x86/lbr: Unify LBR_INFO registers exposure check condition
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 and its XSAVES bit

arch/x86/events/intel/lbr.c | 4 +-
arch/x86/include/asm/vmx.h | 4 ++
arch/x86/kvm/cpuid.c | 19 +++++++++
arch/x86/kvm/vmx/capabilities.h | 16 ++++++-
arch/x86/kvm/vmx/pmu_intel.c | 74 +++++++++++++++++++++++++++++++--
arch/x86/kvm/vmx/vmx.c | 16 ++++++-
arch/x86/kvm/vmx/vmx.h | 3 ++
arch/x86/kvm/x86.c | 6 +++
8 files changed, 133 insertions(+), 9 deletions(-)

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2.21.3