Re: [PATCH] KVM: selftests: Detect max PA width from cpuid

Peter Xu
2019-08-26T08:18:59Z

On Mon, Aug 26, 2019 at 10:11:34AM +0200, Thomas Huth wrote:
> On 26/08/2019 09.57, Peter Xu wrote:
> > The dirty_log_test is failing on some old machines like Xeon E3-1220
> > with tripple faults when writting to the tracked memory region:
> >
> > Test iterations: 32, interval: 10 (ms)
> > Testing guest mode: PA-bits:52, VA-bits:48, 4K pages
> > guest physical test memory offset: 0x7fbffef000
> > ==== Test Assertion Failure ====
> > dirty_log_test.c:138: false
> > pid=6137 tid=6139 - Success
> > 1 0x0000000000401ca1: vcpu_worker at dirty_log_test.c:138
> > 2 0x00007f3dd9e392dd: ?? ??:0
> > 3 0x00007f3dd9b6a132: ?? ??:0
> > Invalid guest sync status: exit_reason=SHUTDOWN
> >
> > It's because previously we moved the testing memory region from a
> > static place (1G) to the top of the system's physical address space,
> > meanwhile we stick to 39 bits PA for all the x86_64 machines. That's
> > not true for machines like Xeon E3-1220 where it only supports 36.
> >
> > Let's unbreak this test by dynamically detect PA width from CPUID
> > 0x80000008. Meanwhile, even allow kvm_get_supported_cpuid_index() to
> > fail. I don't know whether that could be useful because I think
> > 0x80000008 should be there for all x86_64 hosts, but I also think it's
> > not really helpful to assert in the kvm_get_supported_cpuid_index().
> [...]
> > diff --git a/tools/testing/selftests/kvm/lib/x86_64/processor.c b/tools/testing/selftests/kvm/lib/x86_64/processor.c
> > index 6cb34a0fa200..9de2fd310ac8 100644
> > --- a/tools/testing/selftests/kvm/lib/x86_64/processor.c
> > +++ b/tools/testing/selftests/kvm/lib/x86_64/processor.c
> > @@ -760,9 +760,6 @@ kvm_get_supported_cpuid_index(uint32_t function, uint32_t index)
> > break;
> > }
> > }
> > -
> > - TEST_ASSERT(entry, "Guest CPUID entry not found: (EAX=%x, ECX=%x).",
> > - function, index);
> > return entry;
> > }
>
> You should also adjust the comment of the function. It currently says
> "Never returns NULL". Not it can return NULL.

Yeh that's better.

>
> And maybe add a TEST_ASSERT() to the other callers instead, which do not
> expect a NULL to be returned?

I think it's fine because it's the same as moving the assert from here
to the callers because when the caller uses entry->xxx it'll assert. :)

Thanks,

--
Peter Xu