Re: [Xen-devel] Paravirtualization of the "HLT" instruction (for example) on x386

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 12 Jan 2006, at 10:39, Ian Brown wrote:

> 1) Can you please give a pointer to where in code (xen 3.0) such 
> privileged
> instruction is  replaced
> with a trap to the hypervisor ? (I have some assumption where it is 
> done
> but I am really not sure at all)
xen_idle() in arch/xen/i386/process.c. Uses the SCHEDOP_block 
hypercall, which is a fairly direct replacement for HLT.
> 2) Regarding HLT - what happens if a guest OS issue "HLT" ?
> I assume that without intervention in Xen code, issuing HLT from a
> guest domain can stop not only the guest domain, but also the
> hypervisor (and in fact the machine).
> is there somewhere in code special treatment to "HLT"?
HLT is only executable in ring 0. If the guest tries to execute it then 
it will receive a general protection fault.
 -- Keir


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