Avi Kivity wrote:
On 07/07/2009 04:15 PM, Jerry Geis wrote:
Notice FPU indicates yes and I requested -fpu on the command line.
I think it detects the host fpu as a 487 coprocessor. Anything in
dmesg about it? Note there's no fpu in the flags: line.
That's a kvm kernel bug.
also is this a 486 as it says AMD?
You can override it if you like, -cpu 486,vendor=AuthenticAMD (I think).
Sorry - I thought the " -cpu 486,-fpu " was the way to turn off the fpu.
I 'm trying to emulute a 486 sx that has no fpu.
I thought so too, but in fact it emulates a 486sx+487.
-fpu does not help here, as the injected 486 CPUID limits the level to
0, so effectively no other leaf than leaf 0 is checked by the guest.
That's why the FPU bit, which is 0000_0001.EDX:0, is not honored.
I bumped up the level to 1 and set the model to 2, which should mimic a
later 486SX chip, together with -fpu Linux (2.6.21) still insisted on
fpu: yes (probably determined by probing FPU instructions).
> We can make it
emulate a 486sx without a 487, but that will take a kernel patch.
What are you thinking of? Forcing CR0.EM to 1 (and don't let the guest
change it), then inject #NM into the guest?
Regards,
Andre.
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Andre Przywara
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