fix swapping on 8xx?

[Marcelo Tosatti]

Hi, 

The following is an attempt to fix swapping on 8xx by not touching
_PAGE_ACCESSED bit if the page is not present.

Dan, what do you think?


diff --git a/arch/ppc/kernel/head_8xx.S b/arch/ppc/kernel/head_8xx.S
index de09787..4451828 100644
--- a/arch/ppc/kernel/head_8xx.S
+++ b/arch/ppc/kernel/head_8xx.S
@@ -41,6 +41,22 @@
 #else
 #define DO_8xx_CPU6(val, reg)
 #endif
+
+/* can't overwrite the _PAGE_ACCESSED bit of a non-present page (might
+   contain swap data). */
+#ifdef CONFIG_SWAP
+#define SET_PAGE_ACCESSED(reg, destreg, tmpreg)		\
+	andi.	tmpreg, reg, _PAGE_PRESENT;		\
+	beq	9f;					\
+	ori	reg, reg, _PAGE_ACCESSED;		\
+	stw	r10, 0(destreg);			\
+9:
+#else
+#define SET_PAGE_ACCESSED(reg, destreg, tmpreg)	\
+	ori	reg, reg, _PAGE_ACCESSED;	\
+	stw	reg, 0(destreg);
+#endif
+
 	.text
 	.globl	_stext
 _stext:
@@ -332,8 +348,7 @@ InstructionTLBMiss:
 	mfspr	r11, SPRN_MD_TWC	/* ....and get the pte address */
 	lwz	r10, 0(r11)	/* Get the pte */
 
-	ori	r10, r10, _PAGE_ACCESSED
-	stw	r10, 0(r11)
+	SET_PAGE_ACCESSED(r10, r11, r3)
 
 	/* The Linux PTE won't go exactly into the MMU TLB.
 	 * Software indicator bits 21, 22 and 28 must be clear.
@@ -399,8 +414,7 @@ DataStoreTLBMiss:
 	mtspr	SPRN_MD_TWC, r11
 
 	mfspr	r11, SPRN_MD_TWC	/* get the pte address again */
-	ori	r10, r10, _PAGE_ACCESSED
-	stw	r10, 0(r11)
+	SET_PAGE_ACCESSED(r10, r11, r3)	/* and update pte in table */
 
 	/* The Linux PTE won't go exactly into the MMU TLB.
 	 * Software indicator bits 21, 22 and 28 must be clear.
@@ -507,9 +521,9 @@ DataTLBError:
 
 	/* Update 'changed', among others.
 	*/
-	ori	r10, r10, _PAGE_DIRTY|_PAGE_ACCESSED|_PAGE_HWWRITE
+	ori	r10, r10, _PAGE_DIRTY|_PAGE_HWWRITE
 	mfspr	r11, SPRN_MD_TWC		/* Get pte address again */
-	stw	r10, 0(r11)		/* and update pte in table */
+	SET_PAGE_ACCESSED(r10, r11, r3)		/* and update pte in table */
 
 	/* The Linux PTE won't go exactly into the MMU TLB.
 	 * Software indicator bits 21, 22 and 28 must be clear.