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SubjectRe: This can freeze linux 2.0 on 486
> > Recently I saw this behaviour on linux 2.0 running on i486.
> > Instruction invd ( supposed to invalidate cache) can lock the m/c
> > completely.
Alan Cox writes -

> If you can do this from userspace can you try the same with a different
> OS on the same hardware. It might he hardware, it might be trap handling
> it might be a buggy chip or a general flaw in a stepping
> I wouldnt rule out hardware. The 386 can be crashed with an instruction
> from userspace
> Alan

This seems to be the conclusion I would infer too. This is the output
of cat /proc/cpuinfo:
processor : 0
cpu : 486
model : DX/4-WB
vendor_id : AuthenticAMD
stepping : 4
fdiv_bug : no
hlt_bug : no
fpu : yes
fpu_exception : yes
cpuid : yes
wp : yes
flags : fpu
bogomips : 49.86

I tried the same program (containing INVD instruction) on a
486 from Intel, nothing spectular happened. Though I did not get
fault there too, at least no crash. As far as my knowledge goes
INVD should be a privileged instruction on both 486 and Pentium.
AMD can produce such CPUs where a userspace program having invd instruction
can crash the machine. The poor OS can't help if Hardware is buggy.



Praveen Dwivedi

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