[PATCH v2 0/5] perf: KVM: Enable callchains for guests

[Tianyi Liu]

Hi there,

This series of patches enables callchains for guests (used by perf kvm),
which holds the top spot on the perf wiki TODO list [1]. This allows users
to perform guest OS callchain or performance analysis from external
using PMU events.

The event processing flow is as follows (shown as backtrace):
  #0 kvm_arch_vcpu_get_frame_pointer / kvm_arch_vcpu_read_virt (per arch)
  #1 kvm_guest_get_frame_pointer / kvm_guest_read_virt
     <callback function pointers in `struct perf_guest_info_callbacks`>
  #2 perf_guest_get_frame_pointer / perf_guest_read_virt
  #3 perf_callchain_guest
  #4 get_perf_callchain
  #5 perf_callchain

Between #0 and #1 is the interface between KVM and the arch-specific
impl, while between #1 and #2 is the interface between Perf and KVM.
The 1st patch implements #0. The 2nd patch extends interfaces between #1
and #2, while the 3rd patch implements #1. The 4th patch implements #3
and modifies #4 #5. The last patch is for userspace utils.

Since arm64 hasn't provided some foundational infrastructure (interface
for reading from a virtual address of guest), the arm64 implementation
is stubbed for now because it's a bit complex, and will be implemented
later.

Tested with both 32-bit and 64-bit guest operating systems / unikernels,
that `perf script` could correctly show the certain callchains.
FlameGraphs can also be generated with this series of patches and [2].

Any feedback will be greatly appreciated.

[1] https://perf.wiki.kernel.org/index.php/Todo
[2] https://github.com/brendangregg/FlameGraph

v1:
https://lore.kernel.org/kvm/SYYP282MB108686A73C0F896D90D246569DE5A@SYYP282MB1086.AUSP282.PROD.OUTLOOK.COM/

Changes since v1:
- v1 only includes partial KVM modifications, while v2 is a complete
implementation. Also updated based on Sean's feedback.

Tianyi Liu (5):
  KVM: Add arch specific interfaces for sampling guest callchains
  perf kvm: Introduce guest interfaces for sampling callchains
  KVM: implement new perf interfaces
  perf kvm: Support sampling guest callchains
  perf tools: Support PERF_CONTEXT_GUEST_* flags

 arch/arm64/kvm/arm.c                | 17 +++++++++
 arch/x86/events/core.c              | 56 +++++++++++++++++++++++------
 arch/x86/kvm/x86.c                  | 18 ++++++++++
 include/linux/kvm_host.h            |  4 +++
 include/linux/perf_event.h          | 18 +++++++++-
 kernel/bpf/stackmap.c               |  8 ++---
 kernel/events/callchain.c           | 27 +++++++++++++-
 kernel/events/core.c                | 17 ++++++++-
 tools/perf/builtin-timechart.c      |  6 ++++
 tools/perf/util/data-convert-json.c |  6 ++++
 tools/perf/util/machine.c           |  6 ++++
 virt/kvm/kvm_main.c                 | 25 +++++++++++++
 12 files changed, 191 insertions(+), 17 deletions(-)


base-commit: 8a749fd1a8720d4619c91c8b6e7528c0a355c0aa
-- 
2.42.0