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

From: Michael Neuling <[email-masked]>
Date: Fri, 15 Jan 2016 17:04:49 +1100

On Fri, 2016-01-15 at 16:54 +1100, Cyril Bur wrote:
> On Fri, 15 Jan 2016 16:42:22 +1100
> Michael Neuling <[email-masked]> wrote:
>=20
> > 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. =20
> >=20
> > Is this a bug in the current code?
> >=20
>=20
> You're very consistent:
>=20
> https://lists.ozlabs.org/pipermail/linuxppc-dev/2015-November/136469.
> html

Fix the comment to explain why it's not a bug now.

Mikey

> ;)
>=20
> > Mikey
> >=20
> > > Signed-off-by: Cyril Bur <[email-masked]>
> > > ---
> > >  arch/powerpc/kernel/process.c | 1 +
> > >  1 file changed, 1 insertion(+)
> > >=20
> > > 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,
> > > =20
> > >  		f =3D ret_from_fork;
> > >  	}
> > > +	childregs->msr &=3D ~(MSR_FP|MSR_VEC|MSR_VSX);
> > >  	sp -=3D STACK_FRAME_OVERHEAD;
> > > =20
> > >  	/* =20
>=20
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