[PATCH 0/3] ARM: fix hash_name() and branch predictor issues

[Russell King (Oracle)]

This series, which I'm intending to be part of my upcoming pull request
for this merge window (note - will be sent before Thursday, otherwise
it won't be until maybe the middle of January) fixes the recently
reported hash_name() issue, and also the long standing branch predictor
hardening smp_processor_id() warning which occurs due to interrupts
being enabled.

Fixing this isn't trivial because there are many paths through
do_page_fault() which are non-obvious.

For example, we detect page faults by the kernel attempting to execute
memory that it shouldn't and print such a warning. If we introduce an
early address check, we avoid that detection, making it become a
plain kernel oops without the informative error message.

The first patch adds an additional check in __do_kernel_fault() to
detect this condition. This patch is a non-obvious dependency for the
next patch.

The second patch handles faults above the top of userspace entirely
separately, meaning we have a simpler and more obvious fault path,
which avoids any possibility of taking any MM mutexes, which is the
cause of the hash_name() problem.

The third patch moves harden_branch_predictor() out of
__do_user_fault() and to appropriate places in the parent functions.
The reason this has been avoided thus far is because do_page_fault()
can be a hot path (since it's used for page aging as well) but with
kernel address faults being handled by an entirely separate path,
this avoids adding to that overhead.

I would like to get some attributations for this - specifically
tested-by.

Thanks.

 arch/arm/mm/alignment.c |  6 +++-
 arch/arm/mm/fault.c     | 74 +++++++++++++++++++++++++++++++++++++++++--------
 2 files changed, 67 insertions(+), 13 deletions(-)

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