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

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Date:   Thu, 13 Jul 2017 19:49:05 +1000
From:   Balbir Singh <bsingharora@...il.com>
To:     Ram Pai <linuxram@...ibm.com>
Cc:     "open list:LINUX FOR POWERPC (32-BIT AND 64-BIT)" 
        <linuxppc-dev@...ts.ozlabs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        linux-kselftest@...r.kernel.org,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Anshuman Khandual <khandual@...ux.vnet.ibm.com>,
        Aneesh Kumar KV <aneesh.kumar@...ux.vnet.ibm.com>,
        Dave Hansen <dave.hansen@...el.com>,
        "Haren Myneni/Beaverton/IBM" <hbabu@...ibm.com>,
        Arnd Bergmann <arnd@...db.de>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        Jonathan Corbet <corbet@....net>,
        Ingo Molnar <mingo@...hat.com>
Subject: Re: [RFC v5 15/38] powerpc: helper function to read,write
 AMR,IAMR,UAMOR registers

On Thu, Jul 13, 2017 at 5:55 PM, Ram Pai <linuxram@...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@...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.

Nope, build failures are better than run time failures, otherwise the
kernel will split its guts warning and warning here.

Balbir Singh.