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

From: Nadav Amit <nadav.amit@gmail.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: kvm@vger.kernel.org
Subject: Re: [kvm-unit-tests PATCH 3/3] x86: Support environments without test-devices
Date: Tue, 2 Jul 2019 16:56:29 -0700	[thread overview]
Message-ID: <A4764CFE-CA7A-4714-A54A-9E32DC591160@gmail.com> (raw)
In-Reply-To: <954DC323-15B7-4B35-9249-AB03C9D01BB5@gmail.com>

> On Jul 2, 2019, at 4:39 PM, Nadav Amit <nadav.amit@gmail.com> wrote:
> 
>> On Jul 2, 2019, at 11:28 AM, Paolo Bonzini <pbonzini@redhat.com> 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@redhat.com>.
> 
>  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?

Never mind (for now). I’ll have a look at libacpi when I have time.