linux-kernel - Re: [RFC v5 15/38] powerpc: helper function to read,write AMR,IAMR,UAMOR registers

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Message-Id: <20170713075502.GG5525@ram.oc3035372033.ibm.com>
Date:   Thu, 13 Jul 2017 00:55:02 -0700
From:   Ram Pai <linuxram@...ibm.com>
To:     Balbir Singh <bsingharora@...il.com>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org,
        linux-doc@...r.kernel.org, linux-kselftest@...r.kernel.org,
        benh@...nel.crashing.org, paulus@...ba.org, mpe@...erman.id.au,
        khandual@...ux.vnet.ibm.com, aneesh.kumar@...ux.vnet.ibm.com,
        dave.hansen@...el.com, hbabu@...ibm.com, arnd@...db.de,
        akpm@...ux-foundation.org, corbet@....net, mingo@...hat.com
Subject: Re: [RFC v5 15/38] powerpc: helper function to read,write
 AMR,IAMR,UAMOR registers

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@...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@...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.
RP