linux-kernel - Re: [RFC v5 34/38] procfs: display the protection-key number associated with a vma

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Date:   Thu, 13 Jul 2017 07:07:48 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Ram Pai <linuxram@...ibm.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,
        bsingharora@...il.com, hbabu@...ibm.com, arnd@...db.de,
        akpm@...ux-foundation.org, corbet@....net, mingo@...hat.com
Subject: Re: [RFC v5 34/38] procfs: display the protection-key number
 associated with a vma

On 07/13/2017 01:03 AM, Ram Pai wrote:
> On Tue, Jul 11, 2017 at 11:13:56AM -0700, Dave Hansen wrote:
>> On 07/05/2017 02:22 PM, Ram Pai wrote:
>>> +#ifdef CONFIG_PPC64_MEMORY_PROTECTION_KEYS
>>> +void arch_show_smap(struct seq_file *m, struct vm_area_struct *vma)
>>> +{
>>> +	seq_printf(m, "ProtectionKey:  %8u\n", vma_pkey(vma));
>>> +}
>>> +#endif /* CONFIG_PPC64_MEMORY_PROTECTION_KEYS */
>>
>> This seems like kinda silly unnecessary duplication.  Could we just put
>> this in the fs/proc/ code and #ifdef it on ARCH_HAS_PKEYS?
> 
> Well x86 predicates it based on availability of X86_FEATURE_OSPKE.
> 
> powerpc doesn't need that check or any similar check. So trying to
> generalize the code does not save much IMHO.

I know all your hardware doesn't support it. :)

So, for instance, if you are running on a new POWER9 with radix page
tables, you will just always output "ProtectionKey: 0" in every VMA,
regardless?

> maybe have a seperate inline function that does
> seq_printf(m, "ProtectionKey:  %8u\n", vma_pkey(vma));
> and is called from x86 and powerpc's arch_show_smap()?
> At least will keep the string format captured in 
> one single place.

Now that we have two architectures, is there a strong reason we can't
just have an arch_pkeys_enabled(), and stick the seq_printf() back in
generic code?