Date: Thu, 13 Jul 2017 16:29:16 -0700
From: Ram Pai <linuxram@us.ibm.com>
To: Balbir Singh <bsingharora@gmail.com>
Cc: "open list:LINUX FOR POWERPC (32-BIT AND 64-BIT)" 
        <linuxppc-dev@lists.ozlabs.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        linux-arch <linux-arch@vger.kernel.org>, linux-mm <linux-mm@kvack.org>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
        linux-kselftest@vger.kernel.org,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Anshuman Khandual <khandual@linux.vnet.ibm.com>,
        Aneesh Kumar KV <aneesh.kumar@linux.vnet.ibm.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Haren Myneni/Beaverton/IBM <hbabu@us.ibm.com>,
        Arnd Bergmann <arnd@arndb.de>,
        "akpm@linux-foundation.org" <akpm@linux-foundation.org>,
        Jonathan Corbet <corbet@lwn.net>, Ingo Molnar <mingo@redhat.com>
Subject: Re: [RFC v5 15/38] powerpc: helper function to read,write
 AMR,IAMR,UAMOR registers
Reply-To: Ram Pai <linuxram@us.ibm.com>
References: <1499289735-14220-1-git-send-email-linuxram@us.ibm.com>
 <1499289735-14220-16-git-send-email-linuxram@us.ibm.com>
 <20170712152601.3b2f52ed@firefly.ozlabs.ibm.com>
 <20170713075502.GG5525@ram.oc3035372033.ibm.com>
 <CAKTCnzmDd2K0gc=0gvNn7Q_QBPqmQdwppnpU-J9B1AMva7w8sA@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAKTCnzmDd2K0gc=0gvNn7Q_QBPqmQdwppnpU-J9B1AMva7w8sA@mail.gmail.com>
User-Agent: Mutt/1.5.20 (2009-12-10)
Message-Id: <20170713232916.GK5525@ram.oc3035372033.ibm.com>
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 2978
Lines: 84

On Thu, Jul 13, 2017 at 07:49:05PM +1000, Balbir Singh wrote:
> On Thu, Jul 13, 2017 at 5:55 PM, Ram Pai <linuxram@us.ibm.com> wrote:
> > On Wed, Jul 12, 2017 at 03:26:01PM +1000, Balbir Singh wrote:
> >> On Wed,  5 Jul 2017 14:21:52 -0700
> >> Ram Pai <linuxram@us.ibm.com> wrote:
> >>
> >> > Implements helper functions to read and write the key related
> >> > registers; AMR, IAMR, UAMOR.
> >> >
> >> > AMR register tracks the read,write permission of a key
> >> > IAMR register tracks the execute permission of a key
> >> > UAMOR register enables and disables a key
> >> >
> >> > Signed-off-by: Ram Pai <linuxram@us.ibm.com>
> >> > ---
> >> >  arch/powerpc/include/asm/book3s/64/pgtable.h |   60 ++++++++++++++++++++++++++
> >> >  1 files changed, 60 insertions(+), 0 deletions(-)
> >> >
> >> > diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
> >> > index 85bc987..435d6a7 100644
> >> > --- a/arch/powerpc/include/asm/book3s/64/pgtable.h
> >> > +++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
> >> > @@ -428,6 +428,66 @@ static inline void huge_ptep_set_wrprotect(struct mm_struct *mm,
> >> >             pte_update(mm, addr, ptep, 0, _PAGE_PRIVILEGED, 1);
> >> >  }
> >> >
> >> > +#ifdef CONFIG_PPC64_MEMORY_PROTECTION_KEYS
> >> > +
> >> > +#include <asm/reg.h>
> >> > +static inline u64 read_amr(void)
> >> > +{
> >> > +   return mfspr(SPRN_AMR);
> >> > +}
> >> > +static inline void write_amr(u64 value)
> >> > +{
> >> > +   mtspr(SPRN_AMR, value);
> >> > +}
> >> > +static inline u64 read_iamr(void)
> >> > +{
> >> > +   return mfspr(SPRN_IAMR);
> >> > +}
> >> > +static inline void write_iamr(u64 value)
> >> > +{
> >> > +   mtspr(SPRN_IAMR, value);
> >> > +}
> >> > +static inline u64 read_uamor(void)
> >> > +{
> >> > +   return mfspr(SPRN_UAMOR);
> >> > +}
> >> > +static inline void write_uamor(u64 value)
> >> > +{
> >> > +   mtspr(SPRN_UAMOR, value);
> >> > +}
> >> > +
> >> > +#else /* CONFIG_PPC64_MEMORY_PROTECTION_KEYS */
> >> > +
> >> > +static inline u64 read_amr(void)
> >> > +{
> >> > +   WARN(1, "%s called with MEMORY PROTECTION KEYS disabled\n", __func__);
> >> > +   return -1;
> >> > +}
> >>
> >> Why do we need to have a version here if we are going to WARN(), why not
> >> let the compilation fail if called from outside of CONFIG_PPC64_MEMORY_PROTECTION_KEYS?
> >> Is that the intention?
> >
> > I did not want to stop someone; kernel module for example, from calling
> > these interfaces from outside the pkey domain.
> >
> > Either way can be argued to be correct, I suppose.
> 
> Nope, build failures are better than run time failures, otherwise the
> kernel will split its guts warning and warning here.
> 

Well these are helper functions that can be called by anyone under
any situation. I will rather have them defined unconditionally; under
no ifdefs.  No spewing of warnings anymore. The registers will
be read or written as told. It just makes sense that way.

RP

-- 
Ram Pai