[PATCH V5 0/7] KVM: x86/pmu: Add hardware Topdown metrics support

[Zide Chen]

The Top-Down Microarchitecture Analysis (TMA) method is a structured
approach for identifying performance bottlenecks in out-of-order
processors.

Currently, guests support the TMA method by collecting Topdown events
using GP counters, which may trigger multiplexing.  To free up scarce
GP counters, eliminate multiplexing-induced skew, and obtain coherent
Topdown metric ratios, it is desirable to expose fixed counter 3 and
the IA32_PERF_METRICS MSR to guests.

Several attempts have been made to virtualize this under the legacy
vPMU model [1][2][3], but they were unsuccessful.  With the new mediated
vPMU, enabling TMA support in guests becomes much simpler.  It avoids
invasive changes to the perf core, eliminates CPU pinning and
fixed-counter affinity issues, and reduces the latge overhead of
trapping and emulating MSR accesses.

[1] https://lore.kernel.org/kvm/20231031090613.2872700-1-dapeng1.mi@xxxxxxxxxxxxxxx/
[2] https://lore.kernel.org/all/20230927033124.1226509-1-dapeng1.mi@xxxxxxxxxxxxxxx/T/
[3] https://lwn.net/ml/linux-kernel/20221212125844.41157-1-likexu@xxxxxxxxxxx/

Tested on an SPR.  Without this series, only raw topdown.*_slots events
work in the guest, and metric events (e.g. cpu/topdown-bad-spec/) are
not available.

With this series, metric events are visible in the guest.  Run this
command on both host and guest:

$ perf stat --topdown --no-metric-only -- taskset -c 2 perf bench sched messaging

Host results:

# Running 'sched/messaging' benchmark:
# 20 sender and receiver processes per group
# 10 groups == 400 processes run

     Total time: 1.500 [sec]

 Performance counter stats for 'taskset -c 2 perf bench sched messaging':

     4,266,060,558      TOPDOWN.SLOTS:u              #     32.0 %  tma_frontend_bound
                                                     #      5.2 %  tma_bad_speculation
       588,397,905      topdown-retiring:u           #     13.8 %  tma_retiring
                                                     #     49.0 %  tma_backend_bound
     1,376,283,990      topdown-fe-bound:u
     2,096,827,304      topdown-be-bound:u
       217,425,841      topdown-bad-spec:u
         5,050,520      INT_MISC.UOP_DROPPING:u

Rebased to kvm-x86/next: 9d4853b044be

v5 changes:
- patch 3,5,6/7: new patches to handle RDPMC on metrics.
- patch 6/7: remove host_initiated check.
v4 changes:
- patch 3/4: Remove WARN_ON_ONCE() and simply reject the guest accesses
  by checking host_initiated. (Sashiko)
- patch 3/4: Passthru MSR_PERF_METRICS only if has_mediated_pmu is
  true. (Sashiko)
v3 changes:
- patch 2/4: Move the non-contiguous counter filter code to pmu.c (Dapeng)
- patch 3/4: Replace WARN_ON() with WARN_ON_ONCE(). (Dapeng)
- patch 4/4: Change abs() with explicit bounds (sum >= 0xfd && sum <= 0x102).
- Minor comment cleanups.

v2 changes:
- As suggested by Dapeng, implement a new selftest patch.
- Don't advertise fixed counter 3 if the host doesn't support it.
- Minor change in patch 1 to remove a magic number.

v4:
https://lore.kernel.org/kvm/20260623041927.178256-1-zide.chen@xxxxxxxxx/
QEMU:
https://lore.kernel.org/qemu-devel/20260604025546.19378-7-zide.chen@xxxxxxxxx/

Dapeng Mi (2):
  KVM: x86/pmu: Support Intel fixed counter 3 on mediated vPMU
  KVM: x86/pmu: Support PERF_METRICS MSR in mediated vPMU

Mingwei Zhang (1):
  KVM: x86/pmu: Snapshot host IA32_PERF_CAPABILITIES in kvm_host

Zide Chen (4):
  KVM: x86/pmu: Do not map fixed counters >= 3 to generic perf events
  KVM: x86/pmu: Rename and move vcpu_get_perf_capabilities() to pmu.h
  KVM: x86/pmu: Emulate RDPMC on performance metrics
  KVM: selftests: Add perf_metrics and fixed counter 3 tests

 arch/x86/include/asm/kvm_host.h               |  3 +-
 arch/x86/include/asm/msr-index.h              |  1 +
 arch/x86/include/asm/perf_event.h             |  1 +
 arch/x86/kvm/pmu.c                            | 50 +++++++++++--
 arch/x86/kvm/pmu.h                            | 13 ++++
 arch/x86/kvm/vmx/pmu_intel.c                  | 61 ++++++++++++----
 arch/x86/kvm/vmx/pmu_intel.h                  | 10 +--
 arch/x86/kvm/vmx/vmx.c                        | 15 ++--
 arch/x86/kvm/x86.c                            | 14 +++-
 arch/x86/kvm/x86.h                            |  1 +
 tools/arch/x86/include/asm/msr-index.h        |  1 +
 tools/testing/selftests/kvm/include/x86/pmu.h |  3 +
 .../selftests/kvm/x86/pmu_counters_test.c     | 72 +++++++++++++++++--
 13 files changed, 201 insertions(+), 44 deletions(-)

-- 
2.54.0