[PATCH] Emulate sync instruction variants

[James Yang]

On Thu, 4 Jul 2013, Benjamin Herrenschmidt wrote:

> On Thu, 2013-07-04 at 09:31 +0100, David Laight wrote:
> > Do you need to execute 'sync' here?
> > It is worth checking whether the trap entry/exit doesn't
> > do an implicit one for you.
> 
> Not really. It does an implicit isync (more than one even) but not a 
> sync.

The execution of a sync is required because the original sync variant 
instruction is not actually executed, and, per Ben, no other explicit 
sync exists in the exception handler.  If the ISA extends the sync 
instruction using its reserved bits, the intent would also be that 
executing a heavyweight sync is suitably compatible, otherwise they 
should have modified some other synchronization instruction.  This 
patch ensures at least one sync instruction is executed for each sync 
variant instruction executed that triggers a program exception.