Le 07/11/2014 04:37, Scott Wood a écrit :

On Fri, Sep 19, 2014 at 10:36:09AM +0200, LEROY Christophe wrote:

quoted

No need to re-set this bit at each TLB miss. Let's set it in the PTE.

Signed-off-by: Christophe Leroy <redacted>
---
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...

quoted

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