linux-kernel - Re: [PATCH v2 03/15] s390: zcrypt: externalize AP instructions available function

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Date:   Wed, 28 Feb 2018 18:41:55 +0100
From:   Cornelia Huck <cohuck@...hat.com>
To:     Tony Krowiak <akrowiak@...ux.vnet.ibm.com>
Cc:     linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, freude@...ibm.com, schwidefsky@...ibm.com,
        heiko.carstens@...ibm.com, borntraeger@...ibm.com,
        kwankhede@...dia.com, bjsdjshi@...ux.vnet.ibm.com,
        pbonzini@...hat.com, alex.williamson@...hat.com,
        pmorel@...ux.vnet.ibm.com, alifm@...ux.vnet.ibm.com,
        mjrosato@...ux.vnet.ibm.com, jjherne@...ux.vnet.ibm.com,
        thuth@...hat.com, pasic@...ux.vnet.ibm.com,
        fiuczy@...ux.vnet.ibm.com, buendgen@...ibm.com
Subject: Re: [PATCH v2 03/15] s390: zcrypt: externalize AP instructions
 available function

On Tue, 27 Feb 2018 09:28:01 -0500
Tony Krowiak <akrowiak@...ux.vnet.ibm.com> wrote:

> If the AP instructions are not available on the linux host, then
> AP devices can not be interpreted by the SIE. The AP bus has a
> function it uses to determine if the AP instructions are
> available. This patch provides a new function that wraps the
> AP bus's function to externalize it for use by KVM.
> 
> Signed-off-by: Tony Krowiak <akrowiak@...ux.vnet.ibm.com>
> Reviewed-by: Pierre Morel <pmorel@...ux.vnet.ibm.com>
> ---
>  arch/s390/include/asm/ap.h   |    7 +++++++
>  drivers/s390/crypto/ap_bus.c |    6 ++++++
>  2 files changed, 13 insertions(+), 0 deletions(-)

While I don't see anything wrong with this patch as it stands, you need
to be careful to call this only from vfio-ap code (which depends on
CONFIG_ZCRYPT).

Speaking of which: the ap_bus part cannot be a module, but only
built-in, right? So we don't get additional module complications?