[PATCHv2] arm: Preserve TPIDRURW on context switch

[Will Deacon]

On Mon, Apr 22, 2013 at 03:36:16PM +0100, Russell King - ARM Linux wrote:
> On Fri, Apr 19, 2013 at 05:54:35PM +0200, André Hentschel wrote:
> > From: =?UTF-8?q?Andr=C3=A9=20Hentschel?= <nerv at dawncrow.de>
> > 
> > There are more and more applications coming to WinRT, Wine could support them,
> > but mostly they expect to have the thread environment block (TEB) in TPIDRURW.
> > This register must be preserved per thread instead of being cleared.
> > 
> > Signed-off-by: André Hentschel <nerv at dawncrow.de>
> 
> This actually makes things less efficient all round, because you
> now use the value immediately after loading, which means it will cause
> pipeline stalls, certainly on older CPUs.
> 
> Could you please rework the patch to try avoiding soo many modifications
> to the way things have been done here?

copy_thread also needs updating so that the *register* value for the parent
is copied to the child, since the parent may have written the register
after the last context-switch, meaning that tp_value is out-of-date.

Will