Re: [v4,17/21] powerpc/8xx: set PTE bit 22 off TLBmiss

[leroy christophe]

Le 07/11/2014 04:37, Scott Wood a écrit :
> On Fri, Sep 19, 2014 at 10:36:09AM +0200, LEROY Christophe wrote:
> > No need to re-set this bit at each TLB miss. Let's set it in the PTE.
> >
> > Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxx>
> > ---
> > Changes in v2:
> > - None
> >
> > Changes in v3:
> > - Removed PPC405 related macro from PPC8xx specific code
> > - PTE_NONE_MASK doesn't need PAGE_ACCESSED in Linux 2.6
> >
> > Changes in v4:
> > - None
> >
> >   arch/powerpc/include/asm/pgtable-ppc32.h | 20 ++++++++++++++++++++
> >   arch/powerpc/include/asm/pte-8xx.h       |  7 +++++--
> >   arch/powerpc/kernel/head_8xx.S           | 10 ++--------
> >   3 files changed, 27 insertions(+), 10 deletions(-)
> >
> > diff --git a/arch/powerpc/include/asm/pgtable-ppc32.h b/arch/powerpc/include/asm/pgtable-ppc32.h
> > index 47edde8..35a9b44 100644
> > --- a/arch/powerpc/include/asm/pgtable-ppc32.h
> > +++ b/arch/powerpc/include/asm/pgtable-ppc32.h
> > @@ -172,6 +172,25 @@ static inline unsigned long pte_update(pte_t *p,
> >   #ifdef PTE_ATOMIC_UPDATES
> >   	unsigned long old, tmp;
> >   
> > +#ifdef CONFIG_PPC_8xx
> > +	unsigned long tmp2;
> > +
> > +	__asm__ __volatile__("\
> > +1:	lwarx	%0,0,%4\n\
> > +	andc	%1,%0,%5\n\
> > +	or	%1,%1,%6\n\
> > +	/* 0x200 == Extended encoding, bit 22 */ \
> > +	/* Bit 22 has to be 1 if neither _PAGE_USER nor _PAGE_RW are set */ \
> > +	rlwimi	%1,%1,32-2,0x200\n /* get _PAGE_USER */ \
> > +	rlwinm	%3,%1,32-1,0x200\n /* get _PAGE_RW */ \
> > +	or	%1,%3,%1\n\
> > +	xori	%1,%1,0x200\n"
> > +"	stwcx.	%1,0,%4\n\
> > +	bne-	1b"
> Why do you need this...
>
> > diff --git a/arch/powerpc/include/asm/pte-8xx.h b/arch/powerpc/include/asm/pte-8xx.h
> > index d44826e..daa4616 100644
> > --- a/arch/powerpc/include/asm/pte-8xx.h
> > +++ b/arch/powerpc/include/asm/pte-8xx.h
> > @@ -48,19 +48,22 @@
> >    */
> >   #define _PAGE_RW	0x0400	/* lsb PP bits, inverted in HW */
> >   #define _PAGE_USER	0x0800	/* msb PP bits */
> > +/* set when neither _PAGE_USER nor _PAGE_RW are set */
> > +#define _PAGE_KNLRO	0x0200
> >   
> >   #define _PMD_PRESENT	0x0001
> >   #define _PMD_BAD	0x0ff0
> >   #define _PMD_PAGE_MASK	0x000c
> >   #define _PMD_PAGE_8M	0x000c
> >   
> > -#define _PTE_NONE_MASK _PAGE_ACCESSED
> > +#define _PTE_NONE_MASK _PAGE_KNLRO
> >   
> >   /* Until my rework is finished, 8xx still needs atomic PTE updates */
> >   #define PTE_ATOMIC_UPDATES	1
> >   
> >   /* We need to add _PAGE_SHARED to kernel pages */
> > -#define _PAGE_KERNEL_RO	(_PAGE_SHARED)
> > +#define _PAGE_KERNEL_RO	(_PAGE_SHARED | _PAGE_KNLRO)
> > +#define _PAGE_KERNEL_ROX	(_PAGE_EXEC | _PAGE_KNLRO)
> >   #define _PAGE_KERNEL_RW	(_PAGE_DIRTY | _PAGE_RW | _PAGE_HWWRITE)
> ...if 0x200 is already being set in the PTE here?
If I understand well the way it works, those defines are used for 
setting the PTE the first time.
Then, pte_update() is used to modify the pte settings on an existing pte

0x200 must be set when and only when the page is a RO kernel page. If 
later on pte_update() is called for instance to set the page to RW, the 
0x200 has to be removed. Same, if pte_update() is called to remove 
_PAGE_RW (ptep_set_wrprotect() does this), 0x200 must be set back.

Christophe

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