Re: [PATCH kvm-unit-tests 2/3] arm64: timer: Fix test on APM X-Gene

Christoffer Dall
2017-07-24T21:24:52Z

On Mon, Jul 24, 2017 at 7:13 PM, Paolo Bonzini <pbonzini@redhat.com> wrote:
> On 18/07/2017 14:15, Andrew Jones wrote:
>>>
>>> If we want to add a "the platform provides a timer with 56 valid bits in
>>> the counter and compare register", then I think it should be a separate
>>> test, and the the user can see that "basic stuff works", "architecture
>>> compliance not so much" and shrug accordingly.
>> Two separate tests sounds good to me. Although, if the value of 'now' is
>> large enough that now + 10s will set bit 31, then a mustang run (at least
>> mine) will fail - and most likely cause a lot of confusion, since it
>> normally does not. We should probably attempt to address that known issue
>> in some way as well.
>
> Is the value relative to vm startup or host startup?
>
For the virtual timer, KVM currently resets the counter to zero (so VM
startup) and for the physical timer it's since host startup.

I confirmed the behavior Drew reported on my mustang too, but it only
appears to apply for the vtimer when writing cval with bit 31 set, not
for the ptimer. I was thinking that this may be a problem with KVM,
some sort of signed bit extension problem, but since the problem
doesn't show up on other platforms, it may just be a problem there.
Shrug.

Anyway, since it works with the ptimer, and we should have at least 56
bits of counter space at ~50 MHz, we should be fine here.

Thanks,
-Christoffer