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Date:   Mon, 23 Apr 2018 09:04:49 +0200
From:   Cornelia Huck <cohuck@redhat.com>
To:     Tony Krowiak <akrowiak@linux.vnet.ibm.com>
Cc:     Pierre Morel <pmorel@linux.vnet.ibm.com>, freude@de.ibm.com,
        buendgen@de.ibm.com, linux-s390@vger.kernel.org,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        schwidefsky@de.ibm.com, heiko.carstens@de.ibm.com,
        borntraeger@de.ibm.com, kwankhede@nvidia.com,
        bjsdjshi@linux.vnet.ibm.com, pbonzini@redhat.com,
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        mjrosato@linux.vnet.ibm.com, jjherne@linux.vnet.ibm.com,
        thuth@redhat.com, pasic@linux.vnet.ibm.com, berrange@redhat.com,
        fiuczy@linux.vnet.ibm.com
Subject: Re: [PATCH v4 01/15] s390: zcrypt: externalize AP instructions
 available function
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On Sun, 22 Apr 2018 13:21:16 -0400
Tony Krowiak <akrowiak@linux.vnet.ibm.com> wrote:

> On 04/17/2018 12:56 PM, Cornelia Huck wrote:
> > On Tue, 17 Apr 2018 09:31:00 -0400
> > Tony Krowiak <akrowiak@linux.vnet.ibm.com> wrote:
> >  
> >> 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.  
> > I think at the root of this is an unfortunate mixup in the
> > architecture: The format of the crycb changes depending on some ap
> > feature being installed. Providing the crycb does not have anything to
> > do with ap device usage in the host, but we need to issue an ap
> > instruction to get this right. [Correct me if I'm wrong; but that's
> > what I get without being able to consult the actual architecture.]
> >
> > So, exporting *all* of the interfaces is probably not needed anyway. I
> > think it boils down to either "export the interfaces where a mixup
> > happened, and keep the rest to zcrypt only", or "duplicate the
> > instructions for kvm usage".
> >
> > I hope we can find a solution here, as this seems to be one of the main
> > discussion points :/ (FWIW, I think the basic driver interface is sane.)  
> 
> I spoke with Harald Freudenberger and he is going to refactor the AP bus
> code to make the two functions//I need static in the kernel:
> 
> int ap_instructions_installed(void);
> int ap_query_configuration(struct ap_config_info *info);
> //
> >  
> 

Excellent, looking forward to it.