Re: [PATCH] x86/CPU/AMD, mm: Extend with mem_encrypt=sme option

From: Borislav Petkov
Date: Mon Oct 02 2017 - 08:41:34 EST

On Mon, Oct 02, 2017 at 06:32:18AM -0500, Brijesh Singh wrote:
> Because sev_enabled will always be 'false' when we are booting on bare
> metal. Whereas when we are running under hypervisor then this variable
> will be true for the SEV guest, please see [1].

Ok, then. This needs absolutely to be documented. Please add a comment
over sev_enabled's definition.

> Both sev_active() and sme_active() make use of this variable
> hence we will not be able to set the sev_enabled variable on bare
> metal. Basically none of the SEV cases will be executed on bare
> metal -- only thing which we need to take care of is clearing the
> X86_FEATURE_SEV flag so that hypervisor will never launch SEV guest
> when mem_encrypt=sme option is provided.

In that case, you want to disable SEV at the guest loading point,
i.e., sev_guest_init() AFAICT is the earliest time we start prepping
a SEV guest. You can add a __setup() early param which parses
"mem_encrypt=sme", to arch/x86/kernel/cpu/amd.c and which sets a
sev_host_enabled bool or so. sev_guest_init() can then check that
variable before going any further. No need for any of that early parsing

I'll send a patch with the rest of my cleanups ontop of yours later.



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