On Thu, 10 Apr 2025 16:10:43 +0100, Sebastian Ott sebott@redhat.com wrote:

Hey,

I'm seeing consistent failures for the arch_timer_edge_cases selftest one ampere-one(x): ==== Test Assertion Failure ==== arm64/arch_timer_edge_cases.c:170: timer_condition == istatus pid=6277 tid=6277 errno=4 - Interrupted system call 1 0x0000000000403bcf: test_run at arch_timer_edge_cases.c:962 2 0x0000000000401f1f: main at arch_timer_edge_cases.c:1083 3 0x0000ffffa8b2625b: ?? ??:0 4 0x0000ffffa8b2633b: ?? ??:0 5 0x000000000040202f: _start at ??:? 0x1 != 0x0 (timer_condition != istatus)

The (first) test that's failing is from test_timers_in_the_past(): /* Set a timer to counter=0 (in the past) */ test_timer_cval(timer, 0, wm, true, DEF_CNT);

If I understand this correctly then the timer condition is met, an irq should be raised with the istatus bit from SYS_CNTV_CTL_EL0 set.

What the guest gets for SYS_CNTV_CTL_EL0 is 1 (only the enable bit set). KVM also reads 1 in timer_save_state() via read_sysreg_el0(SYS_CNTV_CTL). Is this a HW/FW issue?

My hunch is that this is related to AC03_CPU_14 in [1] (now archived locally for future reference...).

These machines have FEAT_ECV (as a test I disabled that in the kernel but with the same result).

As a hack I set ARCH_TIMER_CTRL_IT_STAT in timer_save_state() when the timer condition is met and set up traps for the register - this lets the testcase succeed.

All with the current upstream kernel - but this is not new, I saw this a couple of months ago but lost access to the machine before I could debug..

Any hints what to do here?

Not a lot to do, assuming this is the actual cause. Similar things happen on my QC box, which has a "remarkable" timer implementation and a bunch of terrible hacks to keep it alive.

On the other hand, I'm not even convinced that this test-case is legit. It seems to rely on the counter being 64bit wide, which is not always the case.

M.

[1] https://amperecomputing.com/assets/AmpereOne_Developer_ER_v0_80_20240823_289...