Re: [PATCH v4] mm, pkey: treat pkey-0 special

[Balbir Singh]

On Fri, Mar 16, 2018 at 9:33 PM, Ram Pai <linuxram@xxxxxxxxxx> wrote:
> Applications need the ability to associate an address-range with some
> key and latter revert to its initial default key. Pkey-0 comes close to
> providing this function but falls short, because the current
> implementation disallows applications to explicitly associate pkey-0 to
> the address range.
>
> Clarify the semantics of pkey-0 and provide the corresponding
> implementation.
>
> Pkey-0 is special with the following semantics.
> (a) it is implicitly allocated and can never be freed. It always exists.
> (b) it is the default key assigned to any address-range.
> (c) it can be explicitly associated with any address-range.
>
> Tested on powerpc only. Could not test on x86.


Ram,

I was wondering if we should check the AMOR values on the ppc side to make sure
that pkey0 is indeed available for use as default. I am still of the
opinion that we
should consider non-0 default pkey in the long run. I'm OK with the patches for
now, but really 0 is not special except for it being the default bit
values present
in the PTE.

The patches themselves look OK to me

Balbir Singh.