Messages in this thread | | | From | Dmitry Vyukov <> | Date | Fri, 22 Jul 2022 11:20:25 +0200 | Subject | Re: [PATCH v3 01/14] perf/hw_breakpoint: Add KUnit test for constraints accounting |
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On Fri, 22 Jul 2022 at 11:10, Will Deacon <will@kernel.org> wrote: > > [adding Will] > > > > On Mon, Jul 04, 2022 at 05:05:01PM +0200, Marco Elver wrote: > > > Add KUnit test for hw_breakpoint constraints accounting, with various > > > interesting mixes of breakpoint targets (some care was taken to catch > > > interesting corner cases via bug-injection). > > > > > > The test cannot be built as a module because it requires access to > > > hw_breakpoint_slots(), which is not inlinable or exported on all > > > architectures. > > > > > > Signed-off-by: Marco Elver <elver@google.com> > > > > As mentioned on IRC, I'm seeing these tests fail on arm64 when applied atop > > v5.19-rc7: > > > > | TAP version 14 > > | 1..1 > > | # Subtest: hw_breakpoint > > | 1..9 > > | ok 1 - test_one_cpu > > | ok 2 - test_many_cpus > > | # test_one_task_on_all_cpus: ASSERTION FAILED at kernel/events/hw_breakpoint_test.c:70 > > | Expected IS_ERR(bp) to be false, but is true > > | not ok 3 - test_one_task_on_all_cpus > > | # test_two_tasks_on_all_cpus: ASSERTION FAILED at kernel/events/hw_breakpoint_test.c:70 > > | Expected IS_ERR(bp) to be false, but is true > > | not ok 4 - test_two_tasks_on_all_cpus > > | # test_one_task_on_one_cpu: ASSERTION FAILED at kernel/events/hw_breakpoint_test.c:70 > > | Expected IS_ERR(bp) to be false, but is true > > | not ok 5 - test_one_task_on_one_cpu > > | # test_one_task_mixed: ASSERTION FAILED at kernel/events/hw_breakpoint_test.c:70 > > | Expected IS_ERR(bp) to be false, but is true > > | not ok 6 - test_one_task_mixed > > | # test_two_tasks_on_one_cpu: ASSERTION FAILED at kernel/events/hw_breakpoint_test.c:70 > > | Expected IS_ERR(bp) to be false, but is true > > | not ok 7 - test_two_tasks_on_one_cpu > > | # test_two_tasks_on_one_all_cpus: ASSERTION FAILED at kernel/events/hw_breakpoint_test.c:70 > > | Expected IS_ERR(bp) to be false, but is true > > | not ok 8 - test_two_tasks_on_one_all_cpus > > | # test_task_on_all_and_one_cpu: ASSERTION FAILED at kernel/events/hw_breakpoint_test.c:70 > > | Expected IS_ERR(bp) to be false, but is true > > | not ok 9 - test_task_on_all_and_one_cpu > > | # hw_breakpoint: pass:2 fail:7 skip:0 total:9 > > | # Totals: pass:2 fail:7 skip:0 total:9 > > > > ... which seems to be becasue arm64 currently forbids per-task > > breakpoints/watchpoints in hw_breakpoint_arch_parse(), where we have: > > > > /* > > * Disallow per-task kernel breakpoints since these would > > * complicate the stepping code. > > */ > > if (hw->ctrl.privilege == AARCH64_BREAKPOINT_EL1 && bp->hw.target) > > return -EINVAL; > > > > ... which has been the case since day one in commit: > > > > 478fcb2cdb2351dc ("arm64: Debugging support") > > > > I'm not immediately sure what would be necessary to support per-task kernel > > breakpoints, but given a lot of that state is currently per-cpu, I imagine it's > > invasive. > > I would actually like to remove HW_BREAKPOINT completely for arm64 as it > doesn't really work and causes problems for other interfaces such as ptrace > and kgdb.
Will it be a localized removal of code that will be easy to revert in future? Or will it touch lots of code here and there? Let's say we come up with a very important use case for HW_BREAKPOINT and will need to make it work on arm64 as well in future.
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