STGI #UD exception

STGI #UD exception

[mythbuster]

Hello all,

AMD manual states about STGI instruction:

"This instruction generates a #UD exception is SVM is not enabled."

However, if I execute in ring-0 the STGI instruction in my system with
EFER.SVME == 0, I receive a #GP exception instead of a #UD exception.
In other test, I just set the SVME bit to 1 and now I receive a #UD
exception! 

Is the manual wrong?

P.S.: My CPU obviously has the SVM extensions (AMD X2 4600+ AM2)
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Re: STGI #UD exception

[Anthony Liguori]

mythbuster wrote:
> Hello all,
> 
> AMD manual states about STGI instruction:
> 
> "This instruction generates a #UD exception is SVM is not enabled."
> 
> However, if I execute in ring-0 the STGI instruction in my system with
> EFER.SVME == 0, I receive a #GP exception instead of a #UD exception.
> In other test, I just set the SVME bit to 1 and now I receive a #UD
> exception! 

So SVM doesn't work at all?  Have you checked to see if it's disabled in 
your BIOS?

Regards,

Anthony Liguori

> Is the manual wrong?
> 
> P.S.: My CPU obviously has the SVM extensions (AMD X2 4600+ AM2)