Re: [PATCH v4 01/15] s390: zcrypt: externalize AP instructions available function

[Tony Krowiak]

On 04/16/2018 08:11 AM, Cornelia Huck wrote:
> On Mon, 16 Apr 2018 10:44:53 +0200
> Pierre Morel <pmorel@xxxxxxxxxxxxxxxxxx> wrote:
>
> > On 15/04/2018 23:22, Tony Krowiak 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@xxxxxxxxxxxxxxxxxx>
> > > Reviewed-by: Pierre Morel <pmorel@xxxxxxxxxxxxxxxxxx>
> > > Reviewed-by: Harald Freudenberger <freude@xxxxxxxxxxxxxxxxxx>
> > > ---
> > >    arch/s390/include/asm/ap.h     |    7 +++++++
> > >    arch/s390/include/asm/kvm-ap.h |   23 +++++++++++++++++++++++
> > >    arch/s390/kvm/Makefile         |    2 +-
> > >    arch/s390/kvm/kvm-ap.c         |   21 +++++++++++++++++++++
> > >    drivers/s390/crypto/ap_bus.c   |    6 ++++++
> > >    5 files changed, 58 insertions(+), 1 deletions(-)
> > >    create mode 100644 arch/s390/include/asm/kvm-ap.h
> > >    create mode 100644 arch/s390/kvm/kvm-ap.c
> > > diff --git a/arch/s390/kvm/kvm-ap.c b/arch/s390/kvm/kvm-ap.c
> > > new file mode 100644
> > > index 0000000..1267588
> > > --- /dev/null
> > > +++ b/arch/s390/kvm/kvm-ap.c
> > > @@ -0,0 +1,21 @@
> > > +// SPDX-License-Identifier: GPL-2.0+
> > > +/*
> > > + * Adjunct Processor (AP) configuration management for KVM guests
> > > + *
> > > + * Copyright IBM Corp. 2018
> > > + *
> > > + * Author(s): Tony Krowiak <akrowia@xxxxxxxxxxxxxxxxxx>
> > > + */
> > > +#include <linux/kernel.h>
> > > +#include <asm/kvm-ap.h>
> > > +#include <asm/ap.h>
> > > +
> > > +int kvm_ap_instructions_installed(void)
> > > +{
> > > +#ifdef CONFIG_ZCRYPT
> > I did not give my R-B for this.
> > please change it or suppress my R-B
> >
> > I think you should review the way you wrap functions
> > calling the AP interface.
> > Having all of them together would simplify code and review.
> I don't like the ifdeffery either (especially as there's more later).

I'm not crazy about it myself (see below)

> Consolidating all functions for querying basic ap capabilities sounds
> like a good idea. What about collecting them in a ap-util file and
> either always building it or selecting it from both zcrypt and kvm?

My preference would be one of the following:

1. All of the interfaces defined in arch/s390/include/asm/ap.h
   are implemented in a file that is built whether ZCRYPT is
   built or not.

2. The drivers/s390/crypto/ap_asm.h file containing the functions
   that execute the AP instructions are made available outside of
   the AP bus, for example; arch/s390/include/asm

I requested this from the maintainer but was told we don't want to
have any crypto adapter support when the host AP functionality is
disabled (CONFIG_ZCRYPT=n). This makes sense, however; I think it is
a bit confusing to have a header file (arch/s390/include/asm/ap.h)
with interfaces that are conditionally built.

This is why I chose the ifdeffery (as you call it) approach. The
only other solution I can conjure is to duplicate the asm code for
the AP instructions needed in KVM and bypass using the AP bus
interfaces.

> > > +	return ap_instructions_installed();
> > > +#else
> > > +	return 0;
> > > +#endif
> > > +}
> > > +EXPORT_SYMBOL(kvm_ap_instructions_installed);
> > > diff --git a/drivers/s390/crypto/ap_bus.c b/drivers/s390/crypto/ap_bus.c
> > > index 35a0c2b..9d108b6 100644
> > > --- a/drivers/s390/crypto/ap_bus.c
> > > +++ b/drivers/s390/crypto/ap_bus.c
> > > @@ -210,6 +210,12 @@ int ap_query_configuration(struct ap_config_info *info)
> > >    }
> > >    EXPORT_SYMBOL(ap_query_configuration);
> > >
> > > +int ap_instructions_installed(void)
> > > +{
> > > +	return (ap_instructions_available() == 0);
> > > +}
> > > +EXPORT_SYMBOL(ap_instructions_installed);
> > > +
> > >    /**
> > >     * ap_init_configuration(): Allocate and query configuration array.
> > >     */