[PATCH v9 00/17] Introduce Architectural LBR for vPMU

Yang Weijiang
2022-02-16T10:26:55Z

The Architectural Last Branch Records (LBRs) is published in release
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, In this KVM series, we impose one restriction for guest Arch LBR:
Guest can only set the same LBR record depth as host, this is due to
the special behavior of MSR_ARCH_LBR_DEPTH: 1) On write to the MSR,
it'll reset all Arch LBR recording MSRs to 0s. 2) XRSTORS resets all
record MSRs to 0s if the saved depth mismatches MSR_ARCH_LBR_DEPTH.

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

[0] https://software.intel.com/sites/default/files/managed/c5/15/architecture-instruction-set-extensions-programming-reference.pdf
[1] https://lore.kernel.org/lkml/1593780569-62993-1-git-send-email-kan.liang@linux.intel.com/

Qemu patch:
https://patchwork.ozlabs.org/project/qemu-devel/cover/20220215195258.29149-1-weijiang.yang@intel.com/

Previous version:
v8: https://lkml.kernel.org/kvm/1629791777-16430-1-git-send-email-weijiang.yang@intel.com/

Changes in v9:
1. Added Arch LBR MSR access interface for userspace.
2. Refactored XSS related dependent patches so that xsaves/xrstors can work for guest.
3. Refactored Arch LBR CTL and DEPTH MSR handling in KVM.
4. Rebased and tested on kernel base-commit: c5d9ae265b10

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 (2):
KVM: x86: Report XSS as an MSR to be saved if there are supported
features
KVM: x86: Load guest fpu state when accessing MSRs managed by XSAVES

Yang Weijiang (9):
KVM: x86: Refresh CPUID on writes to MSR_IA32_XSS
KVM: x86: Add Arch LBR MSRs to msrs_to_save_all list
KVM: x86/pmu: Refactor code to support guest Arch LBR
KVM: x86/vmx: Check Arch LBR config when return perf capabilities
KVM: nVMX: Add necessary Arch LBR settings for nested VM
KVM: x86/vmx: Clear Arch LBREn bit before inject #DB to guest
KVM: x86/vmx: Flip Arch LBREn bit on guest state change
KVM: x86: Add Arch LBR MSR access interface
KVM: x86/cpuid: Advertise 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 | 7 ++
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 | 8 ++
arch/x86/kvm/vmx/nested.c | 7 +-
arch/x86/kvm/vmx/pmu_intel.c | 155 ++++++++++++++++++++++++++++---
arch/x86/kvm/vmx/vmcs12.c | 1 +
arch/x86/kvm/vmx/vmcs12.h | 3 +-
arch/x86/kvm/vmx/vmx.c | 65 ++++++++++++-
arch/x86/kvm/x86.c | 78 +++++++++++++++-
13 files changed, 356 insertions(+), 36 deletions(-)

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2.27.0