Re: [Xen-devel] How to get a few MSR values from userspace?

[Razvan Cojocaru <rzvncj@xxxxxxxxx>]

Hello, thanks for the reply!

> I'm not sure I understand what you are trying to achieve (nor am I
> convinced I know how to help you, but if I don't understand the question
> suffiiciently, I certainly can't advice you on what you can/should do or
> can't/shouldn't do), but what MSR's are we talking about - the guest
> MSR's or the host MSR's?
Sorry if I've not been clear. I want to access the MSRs of a Xen HVM 
guest, from a userspace application running in dom0, with the help of libxc.
Libxc already allows me to inspect the values of several registers, 
including a handful of MSRs, if I call:
xc_domain_hvm_getcontext_partial(xch, domain_id, HVM_SAVE_CODE(CPU),
                                 instance, &hw_ctxt, sizeof hw_ctxt);

and then examine, for example, hw_ctxt.msr_lstar.

What I'd like is to be able to check hw_ctxt.msr_mc0_ctl, for example, 
after the xc_domain_hvm_getcontext_partial().
> Normally, reading MSR's in usermode is not allowed on bare-metal, so not
> sure why you expect this to work in the guest (or Dom0) on top of Xen.
> But maybe you don't actually mean userspace as opposed to "kernel mode"?
I mean accessing a domU's MSRs from dom0 userspace.

Thanks,
Razvan Cojocaru

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