[Xen-devel] xen pv and cpuid

[Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>]

Silly x86 question of the day:

 

Is it true in a PV domain that there is no way (short of binary translation) to trap a userland cpuid instruction into Xen?

 

I found the routine pv_cpuid() in arch/x86/traps.c and assumed that userland cpuid's would find their way into that code, but it appears to not be the case.  After adding some printks and reading the code more closely, I gather that PV OS's somehow get their cpuid instructions replaced with an invalid op so that kernel-land cpuid's do indeed get trapped? Then looking at the Intel SDM I don't see any way to force cpuid at any privilege level to trap (except in an HVM)?

 

(If this is all correct, then I am sadly back to needing userland hypercalls :-(

 

Thanks,

Dan

 

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