[PATCH 15/16] KVM: arm64: selftests: Augment existing timer test to handle variable offsets

[Colton Lewis]

Hi Marc,

First of all, thanks for your previous responses to my comments. Many of
them clarified things I did not fully understand on my own.

As I stated in another email, I've been testing this series on ECV
capable hardware. Things look good but I have been able to reproduce a
consistent assertion failure in this selftest when setting a
sufficiently large physical offset. I have so far not been able to
determine the cause of the failure and wonder if you have any insight as
to what might be causing this and how to debug.

The following example reproduces the error every time I have tried:

mvbbq9:/data/coltonlewis/ecv/arm64-obj/kselftest/kvm# ./aarch64/arch_timer  
-O 0xffff
==== Test Assertion Failure ====
   aarch64/arch_timer.c:239: false
   pid=48094 tid=48095 errno=4 - Interrupted system call
      1  0x4010fb: test_vcpu_run at arch_timer.c:239
      2  0x42a5bf: start_thread at pthread_create.o:0
      3  0x46845b: thread_start at clone.o:0
   Failed guest assert: xcnt >= cval at aarch64/arch_timer.c:151
values: 2500645901305, 2500645961845; 9939, vcpu 0; stage; 3; iter: 2

Observations:

- Failure always occurs at stage 3 or 4 (physical timer stages)
- xcnt_diff_us is always slightly less than 10000, or 10 ms
- Reducing offset size reduces the probability of failure linearly (for
   example, -O 0x8000 will fail close to half the time)
- Failure occurs with a wide range of different period values and
   whether or not migrations happen