Re: Can't boot as Xen dom0 due to commit fe055896

From: Borislav Petkov
Date: Thu Dec 15 2016 - 18:04:41 EST

On Thu, Dec 15, 2016 at 05:56:44PM -0500, Boris Ostrovsky wrote:
> With CONFIG_PARAVIRT (which I suspect you don't have on) cpuid() is a
> call via a pointer, you can see it, for example, if you disassemble
> load_ucode_amd_bsp(). And we don't have paging on yet when we call
> load_ucode_amd_bsp (at least in 32-bit mode).

That's a good catch, you can send me that one as a proper patch with a
commit message and so on...

> Since this happens during AP bringup PV cpuid is available and can be
> checked to see whether we are a guest.

What exactly do I need to check there? CPUID(4), leaf which, reg which?
How do I identify a xen hypervisor properly?

> But I think it may be worthwhile trying to understand why we are
> dying, it hasn't happened until now.

What for? We don't want to run the microcode loader on xen at all.


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