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

From: Dave Hansen
Date: Thu Jul 13 2017 - 10:08:05 EST

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:
>>> +void arch_show_smap(struct seq_file *m, struct vm_area_struct *vma)
>>> +{
>>> + seq_printf(m, "ProtectionKey: %8u\n", vma_pkey(vma));
>>> +}
>> 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,

> 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?