linux-kernel - Re: [RFC Part1 PATCH v3 16/17] X86/KVM: Provide support to create Guest and HV shared per-CPU variables

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Date:   Mon, 4 Sep 2017 19:05:25 +0200
From:   Borislav Petkov <bp@...e.de>
To:     Brijesh Singh <brijesh.singh@....com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-efi@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        kvm@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Tony Luck <tony.luck@...el.com>,
        Piotr Luc <piotr.luc@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Reza Arbab <arbab@...ux.vnet.ibm.com>,
        David Howells <dhowells@...hat.com>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Laura Abbott <labbott@...hat.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Eric Biederman <ebiederm@...ssion.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Jonathan Corbet <corbet@....net>,
        Dave Airlie <airlied@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Arnd Bergmann <arnd@...db.de>, Tejun Heo <tj@...nel.org>,
        Christoph Lameter <cl@...ux.com>
Subject: Re: [RFC Part1 PATCH v3 16/17] X86/KVM: Provide support to create
 Guest and HV shared per-CPU variables

On Fri, Sep 01, 2017 at 05:52:13PM -0500, Brijesh Singh wrote:
>  So far, we have not seen the need for having such functions except
> this cases. The approach we have right now works just fine and not
> sure if its worth adding new functions.

Then put the call to kvm_map_hv_shared_decrypted() into
kvm_smp_prepare_boot_cpu() to denote that you're executing this whole
stuff only once during guest init.

Now you're doing additional jumping-through-hoops with that once static
var just so you can force something which needs to execute only once but
gets called in a per-CPU path.

See what I mean?

> Thoughts ?
> 
> [1] Commit :7f8b7e7 x86/mm: Add support for early encryption/decryption of memory

Add

[core]
        abbrev = 12

to the core section of your .gitconfig.

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--