Re: [PATCH 0/9] tools: Make {clear,set}_bit() atomic for reals

[Paolo Bonzini]

On 11/19/22 02:34, Sean Christopherson wrote:
> For obvious reasons I'd like to route the this through Paolo's tree.
> In theory, taking just patch 5 through tip would work, but creating a
> topic branch seems like the way to go, though maybe I'm being overly
> paranoid.  The current tip/perf/core doesn't have any conflicts, nor does
> it have new set_bit() or clear_bit() users.
>
>   
> Code sitting in kvm/queue for 6.2 adds functionality that relies on
> clear_bit() being an atomic operation.  Unfortunately, despite being
> implemented in atomic.h (among other strong hits that they should be
> atomic), clear_bit() and set_bit() aren't actually atomic (and of course
> I realized this _just_ after everything got queued up).
>
> Move current tools/ users of clear_bit() and set_bit() to the
> double-underscore versions (which tools/ already provides and documents
> as being non-atomic), and then implement clear_bit() and set_bit() as
> actual atomics to fix the KVM selftests bug.
>
> Perf and KVM are the only affected users.  NVDIMM also has test code
> in tools/, but that builds against the kernel proper.  The KVM code is
> well tested and fully audited.  The perf code is lightly tested; if I
> understand the build system, it's probably not even fully compile tested.
>
> Patches 1 and 2 are completely unrelated and are fixes for patches
> sitting in kvm/queue.  Paolo, they can be squashed if you want to rewrite
> history.
>
> Patch 3 fixes a hilarious collision in a KVM ARM selftest that will arise
> when clear_bit() is converted to an atomic.
>
> Patch 4 changes clear_bit() and set_bit() to take an "unsigned long"
> instead of an "int" so that patches 5-6 aren't accompanied by functional
> changes.  I.e. if something in perf is somehow relying on "bit" being a
> signed int, failures will bisect to patch 4 and not to the
> supposed-to-be-a-nop conversion to __clear_bit() and __set_bit().
>
> Patch 5-9 switch perf+KVM and complete the conversion.
>
> Applies on:
>    
>    git://git.kernel.org/pub/scm/virt/kvm/kvm.git queue

Queued, thanks Namhyung for the ACK!

Paolo

> Sean Christopherson (9):
>    KVM: selftests: Add rdmsr_from_l2() implementation in Hyper-V eVMCS
>      test
>    KVM: selftests: Remove unused "vcpu" param to fix build error
>    KVM: arm64: selftests: Enable single-step without a "full" ucall()
>    tools: Take @bit as an "unsigned long" in {clear,set}_bit() helpers
>    perf tools: Use dedicated non-atomic clear/set bit helpers
>    KVM: selftests: Use non-atomic clear/set bit helpers in KVM tests
>    tools: Drop conflicting non-atomic test_and_{clear,set}_bit() helpers
>    tools: Drop "atomic_" prefix from atomic test_and_set_bit()
>    tools: KVM: selftests: Convert clear/set_bit() to actual atomics
>
>   tools/arch/x86/include/asm/atomic.h           |  6 +++-
>   tools/include/asm-generic/atomic-gcc.h        | 13 ++++++-
>   tools/include/asm-generic/bitops/atomic.h     | 15 ++++----
>   tools/include/linux/bitmap.h                  | 34 -------------------
>   tools/perf/bench/find-bit-bench.c             |  2 +-
>   tools/perf/builtin-c2c.c                      |  6 ++--
>   tools/perf/builtin-kwork.c                    |  6 ++--
>   tools/perf/builtin-record.c                   |  6 ++--
>   tools/perf/builtin-sched.c                    |  2 +-
>   tools/perf/tests/bitmap.c                     |  2 +-
>   tools/perf/tests/mem2node.c                   |  2 +-
>   tools/perf/util/affinity.c                    |  4 +--
>   tools/perf/util/header.c                      |  8 ++---
>   tools/perf/util/mmap.c                        |  6 ++--
>   tools/perf/util/pmu.c                         |  2 +-
>   .../util/scripting-engines/trace-event-perl.c |  2 +-
>   .../scripting-engines/trace-event-python.c    |  2 +-
>   tools/perf/util/session.c                     |  2 +-
>   tools/perf/util/svghelper.c                   |  2 +-
>   .../selftests/kvm/aarch64/arch_timer.c        |  2 +-
>   .../selftests/kvm/aarch64/debug-exceptions.c  | 21 ++++++------
>   tools/testing/selftests/kvm/dirty_log_test.c  | 34 +++++++++----------
>   .../selftests/kvm/include/ucall_common.h      |  8 +++++
>   .../testing/selftests/kvm/lib/ucall_common.c  |  2 +-
>   .../selftests/kvm/x86_64/hyperv_evmcs.c       | 13 +++++--
>   .../selftests/kvm/x86_64/hyperv_svm_test.c    |  4 +--
>   .../selftests/kvm/x86_64/hyperv_tlb_flush.c   |  2 +-
>   27 files changed, 102 insertions(+), 106 deletions(-)
>
>
> base-commit: 3321eef4acb51c303f0598d8a8493ca58528a054