linux-kernel - Re: [Part1 PATCH v6 16/17] X86/KVM: Decrypt shared per-cpu variables when SEV is active

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Date:   Tue, 17 Oct 2017 18:23:04 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Brijesh Singh <brijesh.singh@....com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     x86@...nel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [Part1 PATCH v6 16/17] X86/KVM: Decrypt shared per-cpu variables
 when SEV is active

On Tue, Oct 17, 2017 at 10:42:45AM -0500, Brijesh Singh wrote:
> OK, this goes back to your initial feedback during RFC v3 where I tried
> to do similar thing. But since sev_map_percpu_data() uses __init
> functions hence we need to mark the kvm_guest_cpu_init() as __ref but
> you didn't like the idea and asked me to call the sev_map_percpu_data
> from kvm_smp_prepare_boot_cpu() which is already __init.

So looking at this more, I'm wondering how did I miss this: this whole
SEV code doesn't belong in kvm.c but in svm.c! This is AMD-only and
should be there.

Now, for that you need those three percpu variables to not be static but
I think we can do this by adding their declarations to a kvm-internal.h
header which is in arch/x86/kernel/kvm-internal.h, i.e., not in the
include path and only kvm-related units can include it.

@Paolo: thoughts?

Then, you can call sev_map_percpu_data() during module init, i.e.,
svm_init(). Or in one of the init functions you're adding later,
sev_hardware_setup() for example, or so. I.e., one of those init paths.
Because, AFAICT, you want to clear the physical C-bit only once in the
percpu pages.

I think this is much better than the "grafted" situation now.

-- 
Regards/Gruss,
    Boris.

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