Re: [PATCH v2 3/3] paravirt: rename paravirt_enabled to paravirt_legacy

[Borislav Petkov <bp@alien8.de>]

On Sat, Feb 06, 2016 at 12:05:32PM -0800, Andy Lutomirski wrote:
> int __init microcode_init(void)
> {
>         [...]
>         if (paravirt_enabled() || dis_ucode_ldr)
>                 return -EINVAL;
> 
> This is also asking "are we the natively booted kernel?"  This is
> plausibly useful for real.  (Borislav, is this actually necessary?)

There was some breakage on 32-bit pvops with that.

> Seems to me there should be a function is_native_root_kernel() or
> similar.  Obviously it could have false positives and code will have
> to deal with that.  (This also could be entirely wrong.  What code is
> responsible for CPU microcode updates on Xen?  For all I know, dom0 is
> *supposed* to apply microcode updates, in which case that check really
> should be deleted.

So there are two aspects:

- the guest loading the microcode driver. Xen should behave like
qemu+kvm does: emulate the MSR accesses the microcode loader does.

- microcode application on Xen: we've had this before. The hypervisor
should do that (if it doesn't do so already).

So yes, that paravirt_enabled() thing should go away. Even more so if we
have CPUID leaf 0x4... reserved for hypervisors.

-- 
Regards/Gruss,
    Boris.

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