[RFC,00/14] KVM: arm64: Support FEAT_PMUv3 on Apple hardware

Message

Oliver Upton Dec. 3, 2024, 7:32 p.m. UTC

One of the interesting features of some Apple M* parts is an IMPDEF trap
that routes EL1/EL0 accesses of the PMUv3 registers to EL2. This allows
a hypervisor to emulate an architectural PMUv3 on top of the IMPDEF PMU
hardware present in the CPU.

And if you squint, this _might_ look like a CPU erratum :-)

This series takes advantage of these IMPDEF traps to provide PMUv3 to
KVM guests. As a starting point, only expose the fixed CPU cycle counter
and no event counters. Conveniently, this is enough to get Windows
running as a KVM guest on Apple hardware.

I've tried to keep the deviation to a minimum by refactoring some of the
flows used for PMUv3, e.g. computing PMCEID from the arm_pmu bitmap
instead of reading hardware directly.

Sending this as an RFC as there are some obvious open Qs:

 - Does enabling PMUv3 meet the bar for allowing IMPDEF crap to slide
   into KVM?

   I certainly think the answer is 'yes', especially considering this
   enables Windows guests.

 - Do we want to support programmable event counters?

   I'm sitting on some extra patches to do this, which maps a few
   architectural event IDs into the PERF_TYPE_HARDWARE space, allowing
   the perf driver to select the right hardware event ID.

   Deciding on a sensible number of counters in this case is a bit of a
   mess, as the M* PMCs aren't entirely fungible (some events only work
   on specific counters).

Applies to 6.13-rc1. I've only enabled this for M2 as it is the hardware
I have, but it is extremely likely this feature works on other M* parts.

It is also very possible I've broken something for true PMUv3 hardware,
as I've only tested on the M2.

Oliver Upton (14):
  drivers/perf: apple_m1: Refactor event select/filter configuration
  drivers/perf: apple_m1: Support host/guest event filtering
  drivers/perf: apple_m1: Map generic branch events
  KVM: arm64: Compute PMCEID from arm_pmu's event bitmaps
  KVM: arm64: Always allow fixed cycle counter
  KVM: arm64: Use PERF_COUNT_HW_CPU_CYCLES for fixed cycle counter
  KVM: arm64: Use a cpucap to determine if system supports FEAT_PMUv3
  KVM: arm64: Drop kvm_arm_pmu_available static key
  KVM: arm64: Use guard() to cleanup usage of arm_pmus_lock
  KVM: arm64: Move PMUVer filtering into KVM code
  KVM: arm64: Compute synthetic sysreg ESR for Apple PMUv3 traps
  KVM: arm64: Advertise PMUv3 if IMPDEF traps are present
  KVM: arm64: Advertise 0 event counters for IMPDEF PMU
  arm64: Enable IMP DEF PMUv3 traps on Apple M2

 arch/arm64/include/asm/apple_m1_pmu.h   |   1 +
 arch/arm64/include/asm/cpufeature.h     |  28 +----
 arch/arm64/kernel/cpu_errata.c          |  38 ++++++
 arch/arm64/kernel/cpufeature.c          |  19 +++
 arch/arm64/kernel/image-vars.h          |   5 -
 arch/arm64/kvm/arm.c                    |   4 +-
 arch/arm64/kvm/hyp/include/hyp/switch.h |   4 +-
 arch/arm64/kvm/hyp/vhe/switch.c         |  22 ++++
 arch/arm64/kvm/pmu-emul.c               | 159 +++++++++++++++---------
 arch/arm64/kvm/pmu.c                    |  10 +-
 arch/arm64/tools/cpucaps                |   2 +
 drivers/perf/apple_m1_cpu_pmu.c         |  68 ++++++----
 include/kvm/arm_pmu.h                   |  15 +--
 13 files changed, 248 insertions(+), 127 deletions(-)


base-commit: 40384c840ea1944d7c5a392e8975ed088ecf0b37