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 15:35:55 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Brijesh Singh <brijesh.singh@....com>
Cc:     x86@...nel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.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 06:54:52AM -0500, Brijesh Singh wrote:
> Will do. Do you want me to send v7 with that addressed. Because this
> require changes in 3 patches (PATCH 14, 16, 17)

Just send me those three first as a reply to the thread so that I can
test the whole queue everywhere. Or even better, point me to the v7 git
branch once you have it ready.

> The second call is for UP cases. The kvm_smp_prepapre_boot_cpu() is
> called only when CONFIG_SMP is enabled. Am I missing something ?

Yes, you are.

kvm_guest_init() gets called unconditionally from setup_arch(). But then
you said kvm_guest_init() is called before setup_per_cpu_areas() so why
do you need that call there at all? percpu areas are not ready yet, what
makes them ready in the UP case?

IOW, this sev_map_percpu_data() needs to happen only once, during boot.
So call it only once by finding the right spot and not by adding a
second call for the UP case.

AFAICT, it looks the easiest if you put it in kvm_guest_cpu_init() and
do something like:

	if (smp_processor_id() == boot_cpu_data.cpu_index)
		sev_map_percpu_data();

...

-- 
Regards/Gruss,
    Boris.

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