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Re: [PATCH v3 00/16] perf: KVM: Fix, optimize, and clean up callbacks

On 22/09/21 02:05, Sean Christopherson wrote:
Peter, I left the Intel PT mess as-is.  Having to pass a NULL pointer
from KVM arm64 seemed to be a lesser evil than more exports and multiple
registration paths.

This is a combination of ~2 series to fix bugs in the perf+KVM callbacks,
optimize the callbacks by employing static_call, and do a variety of
cleanup in both perf and KVM.

Patch 1 fixes a mostly-theoretical bug where perf can deref a NULL
pointer if KVM unregisters its callbacks while they're being accessed.
In practice, compilers tend to avoid problematic reloads of the pointer
and the PMI handler doesn't lose the race against module unloading,
i.e doesn't hit a use-after-free.

Patches 2 and 3 fix an Intel PT handling bug where KVM incorrectly
eats PT interrupts when PT is supposed to be owned entirely by the host.

Patches 4-9 clean up perf's callback infrastructure and switch to
static_call for arm64 and x86 (the only survivors).

Patches 10-16 clean up related KVM code and unify the arm64/x86 callbacks.

Based on "git://git.kernel.org/pub/scm/virt/kvm/kvm.git queue", commit
680c7e3be6a3 ("KVM: x86: Exit to userspace ...").

Looks nice apart from a couple nits, I will gladly accept a topic branch with both the perf and the KVM parts.



   - Add wrappers for guest callbacks to that stubs can be provided when
     and XEN_PV instead of from top-level arm64/x86. [Paolo]
   - Drop an unnecessary synchronize_rcu() when registering callbacks. [Peter]
   - Retain a WARN_ON_ONCE() when unregistering callbacks if the caller
     didn't provide the correct pointer. [Peter]
   - Rework the static_call patch to move it all to common perf.
   - Add a patch to drop the (un)register stubs, made possible after
     having KVM+XEN_PV select GUEST_PERF_EVENTS.
   - Split dropping guest callback "support" for arm, csky, etc... to a
     separate patch, to make introducing GUEST_PERF_EVENTS cleaner.
v2 (relative to static_call v10):
   - Split the patch into the semantic change (multiplexed ->state) and
     introduction of static_call.
   - Don't use '0' for "not a guest RIP".
   - Handle unregister path.
   - Drop changes for architectures that can be culled entirely.

v2 (relative to v1):
   - https://lkml.kernel.org/r/20210828003558.713983-6-seanjc@xxxxxxxxxx
   - Drop per-cpu approach. [Peter]
   - Fix mostly-theoretical reload and use-after-free with READ_ONCE(),
     WRITE_ONCE(), and synchronize_rcu(). [Peter]
   - Avoid new exports like the plague. [Peter]

   - https://lkml.kernel.org/r/20210827005718.585190-1-seanjc@xxxxxxxxxx

v10 static_call:
   - https://lkml.kernel.org/r/20210806133802.3528-2-lingshan.zhu@xxxxxxxxx

Like Xu (1):
   perf/core: Rework guest callbacks to prepare for static_call support

Sean Christopherson (15):
   perf: Ensure perf_guest_cbs aren't reloaded between !NULL check and
   KVM: x86: Register perf callbacks after calling vendor's
   KVM: x86: Register Processor Trace interrupt hook iff PT enabled in
   perf: Stop pretending that perf can handle multiple guest callbacks
   perf: Drop dead and useless guest "support" from arm, csky, nds32 and
   perf: Add wrappers for invoking guest callbacks
   perf: Force architectures to opt-in to guest callbacks
   perf/core: Use static_call to optimize perf_guest_info_callbacks
   KVM: x86: Drop current_vcpu for kvm_running_vcpu + kvm_arch_vcpu
   KVM: x86: More precisely identify NMI from guest when handling PMI
   KVM: Move x86's perf guest info callbacks to generic KVM
   KVM: x86: Move Intel Processor Trace interrupt handler to vmx.c
   KVM: arm64: Convert to the generic perf callbacks
   KVM: arm64: Drop perf.c and fold its tiny bits of code into arm.c /
   perf: Drop guest callback (un)register stubs

  arch/arm/kernel/perf_callchain.c   | 28 ++------------
  arch/arm64/include/asm/kvm_host.h  |  9 ++++-
  arch/arm64/kernel/perf_callchain.c | 13 ++++---
  arch/arm64/kvm/Kconfig             |  1 +
  arch/arm64/kvm/Makefile            |  2 +-
  arch/arm64/kvm/arm.c               | 11 +++++-
  arch/arm64/kvm/perf.c              | 62 ------------------------------
  arch/arm64/kvm/pmu.c               |  8 ++++
  arch/csky/kernel/perf_callchain.c  | 10 -----
  arch/nds32/kernel/perf_event_cpu.c | 29 ++------------
  arch/riscv/kernel/perf_callchain.c | 10 -----
  arch/x86/events/core.c             | 13 ++++---
  arch/x86/events/intel/core.c       |  5 +--
  arch/x86/include/asm/kvm_host.h    |  7 +++-
  arch/x86/kvm/Kconfig               |  1 +
  arch/x86/kvm/pmu.c                 |  2 +-
  arch/x86/kvm/svm/svm.c             |  2 +-
  arch/x86/kvm/vmx/vmx.c             | 25 +++++++++++-
  arch/x86/kvm/x86.c                 | 58 +++++-----------------------
  arch/x86/kvm/x86.h                 | 17 ++++++--
  arch/x86/xen/Kconfig               |  1 +
  arch/x86/xen/pmu.c                 | 32 +++++++--------
  include/kvm/arm_pmu.h              |  1 +
  include/linux/kvm_host.h           | 10 +++++
  include/linux/perf_event.h         | 41 ++++++++++++++------
  init/Kconfig                       |  4 ++
  kernel/events/core.c               | 39 +++++++++++++------
  virt/kvm/kvm_main.c                | 44 +++++++++++++++++++++
  28 files changed, 235 insertions(+), 250 deletions(-)
  delete mode 100644 arch/arm64/kvm/perf.c



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