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

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Message-Id: <20170713170411.GI5525@ram.oc3035372033.ibm.com>
Date:   Thu, 13 Jul 2017 10:04:11 -0700
From:   Ram Pai <linuxram@...ibm.com>
To:     Dave Hansen <dave.hansen@...el.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 Thu, Jul 13, 2017 at 07:07:48AM -0700, Dave Hansen wrote:
> 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. :)

Wow! you bring a good point which I had not considered yet. I need some
runtime checks for RPT.

But regardless, my above statement is still partially true. x86
predicates it based on availability of X86_FEATURE_OSPKE, and powerpc
should predicate it based on HPT. So we have our own
customized checks. Hence a unified function won't suffice.

> 
> 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?

correct. that looks like the correct approach. Was trying to avoid
touching arch neutral code. But this approach will force me
do so. Will do.

-- 
Ram Pai