Re: [PATCH] x86/boot/compressed/64: Do not corrupt EDX on EFER.LME=1 setting

[Borislav Petkov]

On Wed, Feb 06, 2019 at 02:52:53PM +0300, Kirill A. Shutemov wrote:
> RDMSR in the trampoline code overrides EDX, but we use the register to
> indicate if 5-level paging has to enabled. It leads to failure to boot
> on a 5-level paging machine.
> 
> Preserve EDX on the stack while we are dealing with EFER.

Comment says:

 * Non zero RDX on return means we need to enable 5-level paging.

Is that per-chance refering to struct paging_config which
paging_prepare() returns and on that return rdx contains
paging_config.l5_required which is 1 when 5 level is to be enabled?

If so, is that written somewhere explicitly? Because it is not
immediately clear at least to me why that RDX is live...

Thx.

-- 
Regards/Gruss,
    Boris.

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