Re: OpenBSD 5.0 kernel panic in AMD K10 cpu power state

[Avi Kivity <avi@redhat.com>]

(re-adding cc)


On 11/09/2011 09:35 PM, Walter Haidinger wrote:
> Am 09.11.2011 14:40, schrieb Avi Kivity:
> > Actually, it looks like an OpenBSD bug.  According to the AMD 
> > documentation:
>
> Well, the OpenBSD developers are very confident that is
> a bug in the KVM cpu emulation and _not_ in OpenBSD.
>
> Basically they say that [despite -cpu host], the emulated
> cpu does not look like a real, but _non-existant_ cpu.
> Virtualization should look like _existing_ hardware.

That is true.  But OpenBSD is not following the vendor's recommendation
for how software should access the hardware.

> Since the list archive at 
> http://marc.info/?l=openbsd-misc&m=132077741910464&w=2
> lags a bit, I'm attaching some parts of the thread below:
>
> However, please remember it's OpenBSD, so the tone is, let's just
> say, rough.

Less than expected, actually.

> > The panic you hit is for an msr read, not a write. I'm aware those 
> > registers are read-only. The CPUID check isn't done, it matches on 
> > all family 10 and/or higher AMD processors. They're pretending to be
> >  an AMD K10 processor. On all real hardware I've tested this works 
> > fine. If you wish to be pedantic, patches are welcome.

So they're actually open to adding the cpuid check.

> They sent me a patch as a workaround, which:
>
> > The previous patch avoids touching the msr at all if ACPI indicates 
> > speed scaling is unavailable, this should prevent your panic.
>
> with -cpu host, OpenBSD dmesg showed the 1100T:
> >> cpu0: AMD Phenom(tm) II X6 1100T Processor ("AuthenticAMD" 686-class, 512KB L2 cache) 3.31 GHz cpu0:
> >> FPU,V86,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,CFLUSH,MMX,FXSR,SSE,SSE2,SSE3,CX16,POPCNT
> >> ...
> >> bios0: vendor Bochs version "Bochs" date 01/01/2007 bios0: Bochs
> >> Bochs
> > They shouldn't be pretending to be AMD, especially if that emulation
> > is very incompatible.
>
> but the bug is in the Linux KVM:
>
> >> They're pretending to be an AMD K10 processor.
> >> 
> > Exactly.  What they are doing is wrong. They are pretending to be a 
> > AMD K10 processor _badly_, and then they think they can say "oh, but 
> > you need to check all these other registers too". A machine with that
> > setup has never physically existed.
>
> Is this all because I used -cpu host? 
>

-cpu host is not to blame, you could get the same result from other
combinations of cpu model and family.

I'll look at adding support for this MSR; should be simple.  But in
general processor features need to be qualified by cpuid, not by model.

-- 
error compiling committee.c: too many arguments to function