linux-kernel - Re: [PATCH v1 03/16] powerpc/32: move LOAD_MSR_KERNEL() into head

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Date:   Mon, 11 Feb 2019 19:06:58 +1100
From:   Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:     Christophe Leroy <christophe.leroy@....fr>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v1 03/16] powerpc/32: move LOAD_MSR_KERNEL() into
 head_32.h and use it

On Mon, 2019-02-11 at 07:26 +0100, Christophe Leroy wrote:
> 
> Le 11/02/2019 à 01:21, Benjamin Herrenschmidt a écrit :
> > On Fri, 2019-02-08 at 12:52 +0000, Christophe Leroy wrote:
> > >   /*
> > > + * MSR_KERNEL is > 0x8000 on 4xx/Book-E since it include MSR_CE.
> > > + */
> > > +.macro __LOAD_MSR_KERNEL r, x
> > > +.if \x >= 0x8000
> > > +       lis \r, (\x)@h
> > > +       ori \r, \r, (\x)@l
> > > +.else
> > > +       li \r, (\x)
> > > +.endif
> > > +.endm
> > > +#define LOAD_MSR_KERNEL(r, x) __LOAD_MSR_KERNEL r, x
> > > +
> > 
> > You changed the limit from >= 0x10000 to >= 0x8000 without a
> > corresponding explanation as to why...
> 
> Yes, the existing LOAD_MSR_KERNEL() was buggy because 'li' takes a 
> signed u16, ie between -0x8000 and 0x7999.

Ah yes, I was only looking at the "large" case which is fine...

> By chance it was working because until now nobody was trying to set 
> MSR_KERNEL | MSR_EE.
> 
> Christophe