Re: [kvm-unit-tests PATCH 3/3] x86: Support environments without test-devices

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> On Jul 2, 2019, at 11:28 AM, Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
> 
> On 02/07/19 19:45, Nadav Amit wrote:
>>>> I know you are not “serious”, but I’ll use this opportunity for a small
>>>> clarification. You do need to provide the real number of CPUs as otherwise
>>>> things will fail. I do not use cpuid, as my machine, for example has two
>>>> sockets. Decoding the ACPI tables is the right way, but I was too lazy to
>>>> implement it.
>>> What about the mptables, too?
>> If you mean to reuse mptable.c from [1] or [2] - I can give it a shot. I am
>> not about to write my own parser.
> 
> Sure.

So mptable logic works on a couple of my machines, but not all.

For instance, on my Dell R630, running x86info (which uses mptable.c), I
get:

  x86info v1.31pre  Dave Jones 2001-2011
  Feedback to <davej@xxxxxxxxxx>.

  Found 48 identical CPUsMP Configuration Table Header MISSING!

And this message (corrupted, but indicates what the code does), is since
apparently the "MP Floating Pointer Structure” holds a zeroed physical
address pointer. (The number 48 comes from sysconf, and clearly not usable
in kvm-unit-tests.)

I also enable apic debugging and had a look on Linux's mpparse outputs. It
does not find the MPF either. 

So it seems to me that it is down to either doing a more comprehensive ACPI
table decoding or having a fallback in the form of a kernel parameter. I am
not really excited about implementing the ACPI option, since I am afraid a
basic implementation will encounter some issues on some machines, similarly
to mptable. The other option is having a fallback as a test parameter, but
if there is already a fallback, then using mptable becomes an enhancement,
and can be left out right now.

What do you say?



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