Subject: Re: [PATCH V2 4/8] powerpc: Explicitly disable math features when copying thread

From: Cyril Bur <[email-masked]>
Date: Fri, 15 Jan 2016 16:54:16 +1100

On Fri, 15 Jan 2016 16:42:22 +1100
Michael Neuling <[email-masked]> wrote:

> On Fri, 2016-01-15 at 16:04 +1100, Cyril Bur wrote:
> > With threads leaving the math bits enabled in their saved MSR to indicate
> > that the hardware is hot and a restore is not needed, children need to turn
> > it off as when they do get scheduled, there's no way their registers could
> > have been hot.  
> 
> Is this a bug in the current code?
> 

You're very consistent:

https://lists.ozlabs.org/pipermail/linuxppc-dev/2015-November/136469.html

;)

> Mikey
> 
> > Signed-off-by: Cyril Bur <[email-masked]>
> > ---
> >  arch/powerpc/kernel/process.c | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/arch/powerpc/kernel/process.c
> > b/arch/powerpc/kernel/process.c
> > index dccc87e..e0c3d2d 100644
> > --- a/arch/powerpc/kernel/process.c
> > +++ b/arch/powerpc/kernel/process.c
> > @@ -1307,6 +1307,7 @@ int copy_thread(unsigned long clone_flags,
> > unsigned long usp,
> >  
> >  		f = ret_from_fork;
> >  	}
> > +	childregs->msr &= ~(MSR_FP|MSR_VEC|MSR_VSX);
> >  	sp -= STACK_FRAME_OVERHEAD;
> >  
> >  	/*