[PATCH V7 00/18] KVM: x86/pmu: Add *basic* support to enable guest PEBS via DS

Zhu Lingshan
2021-06-22T09:43:21Z

The guest Precise Event Based Sampling (PEBS) feature can provide an architectural state of the instruction executed after the guest instruction that exactly caused the event. It needs new hardware facility only available on Intel Ice Lake Server platforms. This patch set enables the basic PEBS feature for KVM guests on ICX.

We can use PEBS feature on the Linux guest like native:

# echo 0 > /proc/sys/kernel/watchdog (on the host)
# perf record -e instructions:ppp ./br_instr a
# perf record -c 100000 -e instructions:pp ./br_instr a

To emulate guest PEBS facility for the above perf usages, we need to implement 2 code paths:

1) Fast path

This is when the host assigned physical PMC has an identical index as the virtual PMC (e.g. using physical PMC0 to emulate virtual PMC0).
This path is used in most common use cases.

2) Slow path

This is when the host assigned physical PMC has a different index from the virtual PMC (e.g. using physical PMC1 to emulate virtual PMC0) In this case, KVM needs to rewrite the PEBS records to change the applicable counter indexes to the virtual PMC indexes, which would otherwise contain the physical counter index written by PEBS facility, and switch the counter reset values to the offset corresponding to the physical counter indexes in the DS data structure.

The previous version [0] enables both fast path and slow path, which seems a bit more complex as the first step. In this patchset, we want to start with the fast path to get the basic guest PEBS enabled while keeping the slow path disabled. More focused discussion on the slow path [1] is planned to be put to another patchset in the next step.

Compared to later versions in subsequent steps, the functionality to support host-guest PEBS both enabled and the functionality to emulate guest PEBS when the counter is cross-mapped are missing in this patch set (neither of these are typical scenarios).

With the basic support, the guest can retrieve the correct PEBS information from its own PEBS records on the Ice Lake servers.
And we expect it should work when migrating to another Ice Lake and no regression about host perf is expected.

Here are the results of pebs test from guest/host for same workload:

perf report on guest:
# Samples: 2K of event 'instructions:ppp', # Event count (approx.): 1473377250 # Overhead Command Shared Object Symbol
57.74% br_instr br_instr [.] lfsr_cond
41.40% br_instr br_instr [.] cmp_end
0.21% br_instr [kernel.kallsyms] [k] __lock_acquire

perf report on host:
# Samples: 2K of event 'instructions:ppp', # Event count (approx.): 1462721386 # Overhead Command Shared Object Symbol
57.90% br_instr br_instr [.] lfsr_cond
41.95% br_instr br_instr [.] cmp_end
0.05% br_instr [kernel.vmlinux] [k] lock_acquire
Conclusion: the profiling results on the guest are similar tothat on the host.

A minimum guest kernel version may be v5.4 or a backport version support Icelake server PEBS.

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

Previous:
https://lore.kernel.org/kvm/20210511024214.280733-1-like.xu@linux.intel.com/

[0]
https://lore.kernel.org/kvm/20210104131542.495413-1-like.xu@linux.intel.com/
[1]
https://lore.kernel.org/kvm/20210115191113.nktlnmivc3edstiv@two.firstfloor.org/

V6 -> V7 Changelog:
- Fix conditions order and call x86_pmu_handle_guest_pebs() unconditionally; (PeterZ)
- Add a new patch to make all that perf_guest_cbs stuff suck less; (PeterZ)
- Document IA32_MISC_ENABLE[7] that that behavior matches bare metal; (Sean & Venkatesh)
- Update commit message for fixed counter mask refactoring;(PeterZ)
- Clarifying comments about {.host and .guest} for intel_guest_get_msrs(); (PeterZ)
- Add pebs_capable to store valid PEBS_COUNTER_MASK value; (PeterZ)
- Add more comments for perf's precise_ip field; (Andi & PeterZ)
- Refactor perf_overflow_handler_t and make it more legible; (PeterZ)
- Use "(unsigned long)cpuc->ds" instead of __this_cpu_read(cpu_hw_events.ds); (PeterZ)
- Keep using "(struct kvm_pmu *)data" to follow K&R; (Andi)

Like Xu (17):
perf/core: Use static_call to optimize perf_guest_info_callbacks
perf/x86/intel: Add EPT-Friendly PEBS for Ice Lake Server
perf/x86/intel: Handle guest PEBS overflow PMI for KVM guest
perf/x86/core: Pass "struct kvm_pmu *" to determine the guest values
KVM: x86/pmu: Set MSR_IA32_MISC_ENABLE_EMON bit when vPMU is enabled
KVM: x86/pmu: Introduce the ctrl_mask value for fixed counter
KVM: x86/pmu: Add IA32_PEBS_ENABLE MSR emulation for extended PEBS
KVM: x86/pmu: Reprogram PEBS event to emulate guest PEBS counter
KVM: x86/pmu: Adjust precise_ip to emulate Ice Lake guest PDIR counter
KVM: x86/pmu: Add IA32_DS_AREA MSR emulation to support guest DS
KVM: x86/pmu: Add PEBS_DATA_CFG MSR emulation to support adaptive PEBS
KVM: x86: Set PEBS_UNAVAIL in IA32_MISC_ENABLE when PEBS is enabled
KVM: x86/pmu: Move pmc_speculative_in_use() to arch/x86/kvm/pmu.h
KVM: x86/pmu: Disable guest PEBS temporarily in two rare situations
KVM: x86/pmu: Add kvm_pmu_cap to optimize perf_get_x86_pmu_capability
KVM: x86/cpuid: Refactor host/guest CPU model consistency check
KVM: x86/pmu: Expose CPUIDs feature bits PDCM, DS, DTES64

Peter Zijlstra (Intel) (1):
x86/perf/core: Add pebs_capable to store valid PEBS_COUNTER_MASK value

arch/arm/kernel/perf_callchain.c | 16 +--
arch/arm64/kernel/perf_callchain.c | 29 +++--
arch/arm64/kvm/perf.c | 22 ++--
arch/csky/kernel/perf_callchain.c | 4 +-
arch/nds32/kernel/perf_event_cpu.c | 16 +--
arch/riscv/kernel/perf_callchain.c | 4 +-
arch/x86/events/core.c | 43 ++++++--
arch/x86/events/intel/core.c | 165 +++++++++++++++++++++++------
arch/x86/events/perf_event.h | 6 +-
arch/x86/include/asm/kvm_host.h | 18 +++-
arch/x86/include/asm/msr-index.h | 6 ++
arch/x86/include/asm/perf_event.h | 5 +-
arch/x86/kvm/cpuid.c | 24 ++---
arch/x86/kvm/cpuid.h | 5 +
arch/x86/kvm/pmu.c | 60 ++++++++---
arch/x86/kvm/pmu.h | 38 +++++++
arch/x86/kvm/vmx/capabilities.h | 26 +++--
arch/x86/kvm/vmx/pmu_intel.c | 115 ++++++++++++++++----
arch/x86/kvm/vmx/vmx.c | 24 ++++-
arch/x86/kvm/vmx/vmx.h | 2 +-
arch/x86/kvm/x86.c | 51 +++++----
arch/x86/xen/pmu.c | 33 +++---
include/linux/perf_event.h | 12 ++-
kernel/events/core.c | 9 ++
24 files changed, 544 insertions(+), 189 deletions(-)

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2.27.0