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Date: Mon, 25 Jul 2022 13:00:48 +0200 From: Marco Elver <elver@...gle.com> To: Mark Rutland <mark.rutland@....com> Cc: Peter Zijlstra <peterz@...radead.org>, Frederic Weisbecker <frederic@...nel.org>, Ingo Molnar <mingo@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, Arnaldo Carvalho de Melo <acme@...nel.org>, Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...hat.com>, Namhyung Kim <namhyung@...nel.org>, Dmitry Vyukov <dvyukov@...gle.com>, Michael Ellerman <mpe@...erman.id.au>, linuxppc-dev@...ts.ozlabs.org, linux-perf-users@...r.kernel.org, x86@...nel.org, linux-sh@...r.kernel.org, kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org, Will Deacon <will@...nel.org> Subject: Re: [PATCH v3 01/14] perf/hw_breakpoint: Add KUnit test for constraints accounting On Thu, 21 Jul 2022 at 18:22, Mark Rutland <mark.rutland@....com> wrote: > > Hi Marco, > > [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@...gle.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. Thanks for investigating - so the test is working as intended. ;-) However it's a shame that arm64's support is limited. And what Will said about possible removal/rework of arm64 hw_breakpoint support doesn't sound too reassuring. We will definitely want to revisit arm64's hw_breakpoint support in future. Thanks, -- Marco
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