[PATCH v9 08/13] arch/arm64: adopt prepare_exit_to_usermode() model from x86

On Mon, Jan 04, 2016 at 04:01:05PM -0500, Chris Metcalf wrote:

On 01/04/2016 03:33 PM, Mark Rutland wrote:

quoted

Hi,

On Mon, Jan 04, 2016 at 02:34:46PM -0500, Chris Metcalf wrote:

quoted

This change is a prerequisite change for TASK_ISOLATION but also
stands on its own for readability and maintainability.

I have also been looking into converting the userspace return path from
assembly to C [1], for the latter two reasons. Based on that, I have a
couple of comments.

Thanks!

quoted

It seems unfortunate to leave behind portions of the entry.S
_TIF_WORK_MASK state machine (i.e. a small portion of ret_fast_syscall,
and the majority of work_pending and ret_to_user).

I think it would be nicer if we could handle all of that in one place
(or at least all in C).

Yes, in principle I agree with this, and I think your deasm tree looks
like an excellent idea.

For this patch series I wanted to focus more on what was necessary
for the various platforms to implement task isolation, and less on
additional cleanups of the platforms in question.  I think my changes
don't make the TIF state machine any less clear, nor do they make
it harder for an eventual further migration to C code along the lines
of what you've done, so it seems plausible to me to commit them
upstream independently of your work.

I appreciate that you don't want to rewrite all the code.

However, I think it's easier to factor out a small amount of additional
code now and evlove that as a whole than it will be to evolve part of it
and try to put it back together later.

I have a patch which I will reply with momentarily.

Thanks,
Mark.