On Thu, Jul 21, 2022 at 05:22:07PM +0100, Mark Rutland wrote:
Hi Marco,
[adding Will]
On Mon, Jul 04, 2022 at 05:05:01PM +0200, Marco Elver wrote:
quoted
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