Re: New CPUID/MSR driver; virtualization hooks

[Zachary Amsden <zach@vmware.com>]

H. Peter Anvin wrote:
>
> This code is almost entirely identical to the setgpr_wrapper in the 
> patch (except for the fact that setgpr_wrapper sets and captures *ALL* 
> the GPRs), and it seems rather pointless to use another wrapper.  It 
> takes a pointer to an entrypoint (default to "cpuid; ret" in the CPUID 
> case), so it should do what you need.

 void (*cpuid)(unsigned int *eax, unsigned int *ebx, ...)

Not quite.  The paravirt_ops CPUID function is a C function which takes 
pointers to each GPR as arguments, and returns the values through those 
pointers.  This doesn't allow for an entrypoint compatible with 
setgpr_wrapper, which expects the same output in both the cpuid; ret 
case and the paravirt-ops case.

One could argue that the paravirt-ops CPUID should in fact emulate the 
native instruction semantics, which would make it a non-C function.  
However, until that bridge is crossed, we would need another wrapper 
after setgpr to convert the paravirt-ops CPUID back into the same format 
as native so that setgpr_wrapper can properly store the output fields 
into the common  i386/x86_64 structure.  What definitely should be done 
is hide this secondary wrapper in the paravirt-ops code so that your 
setgpr wrapper doesn't have to deal with weird issues like this because 
of paravirt-ops changes.

Zach