Re: [PATCH] mm: only enable sys_pkey* when ARCH_HAS_PKEYS

On 10/31/2016 05:08 PM, Mark Rutland wrote:

When an architecture does not select CONFIG_ARCH_HAS_PKEYS, the pkey_alloc
syscall will return -ENOSPC for all (otherwise well-formed) requests, as the
generic implementation of mm_pkey_alloc() returns -1. The other pkey syscalls
perform some work before always failing, in a similar fashion.

This implies the absence of keys, but otherwise functional pkey support. This
is odd, since the architecture provides no such support. Instead, it would be
preferable to indicate that the syscall is not implemented, since this is
effectively the case.

This makes the behavior of an x86 cpu without pkeys and an arm cpu
without pkeys differ.  Is that what we want?  An application that
_wants_ to use protection keys but can't needs to handle -ENOSPC anyway.

On an architecture that will never support pkeys, it makes sense to do
-ENOSYS, but that's not the case for arm, right?