Subject: Re: [PATCH] fixes for the SLB shadow buffer

From: Michael Neuling <[email-masked]>
Date: Fri, 03 Aug 2007 11:55:39 +1000

We sometimes change the vmalloc segment in slb_flush_and_rebolt but we
never updated with slb shadow buffer.  This fixes it.  Thanks to paulus
for finding this.

Also added some write barriers to ensure the shadow buffer is always
valid.

Signed-off-by: Michael Neuling <[email-masked]>
---
Integrated more comments from people.

 arch/powerpc/kernel/entry_64.S   |    3 +++
 arch/powerpc/mm/hash_utils_64.c  |    2 +-
 arch/powerpc/mm/slb.c            |   28 ++++++++++++++++++----------
 include/asm-powerpc/mmu-hash64.h |    1 +
 4 files changed, 23 insertions(+), 11 deletions(-)

Index: linux-2.6-ozlabs/arch/powerpc/kernel/entry_64.S
===================================================================
--- linux-2.6-ozlabs.orig/arch/powerpc/kernel/entry_64.S
+++ linux-2.6-ozlabs/arch/powerpc/kernel/entry_64.S
@@ -389,8 +389,11 @@ BEGIN_FTR_SECTION
 	ld	r9,PACA_SLBSHADOWPTR(r13)
 	li	r12,0
 	std	r12,SLBSHADOW_STACKESID(r9) /* Clear ESID */
+	eieio
 	std	r7,SLBSHADOW_STACKVSID(r9)  /* Save VSID */
+	eieio
 	std	r0,SLBSHADOW_STACKESID(r9)  /* Save ESID */
+	eieio
 
 	slbie	r6
 	slbie	r6		/* Workaround POWER5 < DD2.1 issue */
Index: linux-2.6-ozlabs/arch/powerpc/mm/hash_utils_64.c
===================================================================
--- linux-2.6-ozlabs.orig/arch/powerpc/mm/hash_utils_64.c
+++ linux-2.6-ozlabs/arch/powerpc/mm/hash_utils_64.c
@@ -759,7 +759,7 @@ int hash_page(unsigned long ea, unsigned
 		   mmu_psize_defs[mmu_vmalloc_psize].sllp) {
 		get_paca()->vmalloc_sllp =
 			mmu_psize_defs[mmu_vmalloc_psize].sllp;
-		slb_flush_and_rebolt();
+		slb_vmalloc_update();
 	}
 #endif /* CONFIG_PPC_64K_PAGES */
 
Index: linux-2.6-ozlabs/arch/powerpc/mm/slb.c
===================================================================
--- linux-2.6-ozlabs.orig/arch/powerpc/mm/slb.c
+++ linux-2.6-ozlabs/arch/powerpc/mm/slb.c
@@ -53,7 +53,8 @@ static inline unsigned long mk_vsid_data
 	return (get_kernel_vsid(ea) << SLB_VSID_SHIFT) | flags;
 }
 
-static inline void slb_shadow_update(unsigned long esid, unsigned long vsid,
+static inline void slb_shadow_update(unsigned long ea,
+				     unsigned long flags,
 				     unsigned long entry)
 {
 	/*
@@ -61,11 +62,11 @@ static inline void slb_shadow_update(uns
 	 * updating it.
 	 */
 	get_slb_shadow()->save_area[entry].esid = 0;
-	barrier();
-	get_slb_shadow()->save_area[entry].vsid = vsid;
-	barrier();
-	get_slb_shadow()->save_area[entry].esid = esid;
-
+	smp_wmb();
+	get_slb_shadow()->save_area[entry].vsid = mk_vsid_data(ea, flags);
+	smp_wmb();
+	get_slb_shadow()->save_area[entry].esid = mk_esid_data(ea, entry);
+	smp_wmb();
 }
 
 static inline void create_shadowed_slbe(unsigned long ea, unsigned long flags,
@@ -76,8 +77,7 @@ static inline void create_shadowed_slbe(
 	 * we don't get a stale entry here if we get preempted by PHYP
 	 * between these two statements.
 	 */
-	slb_shadow_update(mk_esid_data(ea, entry), mk_vsid_data(ea, flags),
-			  entry);
+	slb_shadow_update(ea, flags, entry);
 
 	asm volatile("slbmte  %0,%1" :
 		     : "r" (mk_vsid_data(ea, flags)),
@@ -104,8 +104,7 @@ void slb_flush_and_rebolt(void)
 		ksp_esid_data &= ~SLB_ESID_V;
 
 	/* Only third entry (stack) may change here so only resave that */
-	slb_shadow_update(ksp_esid_data,
-			  mk_vsid_data(ksp_esid_data, lflags), 2);
+	slb_shadow_update(get_paca()->kstack, lflags, 2);
 
 	/* We need to do this all in asm, so we're sure we don't touch
 	 * the stack between the slbia and rebolting it. */
@@ -123,6 +122,15 @@ void slb_flush_and_rebolt(void)
 		     : "memory");
 }
 
+void slb_vmalloc_update(void)
+{
+	unsigned long vflags;
+
+	vflags = SLB_VSID_KERNEL | mmu_psize_defs[mmu_vmalloc_psize].sllp;
+	slb_shadow_update(VMALLOC_START, vflags, 1);
+	slb_flush_and_rebolt();
+}
+
 /* Flush all user entries from the segment table of the current processor. */
 void switch_slb(struct task_struct *tsk, struct mm_struct *mm)
 {
Index: linux-2.6-ozlabs/include/asm-powerpc/mmu-hash64.h
===================================================================
--- linux-2.6-ozlabs.orig/include/asm-powerpc/mmu-hash64.h
+++ linux-2.6-ozlabs/include/asm-powerpc/mmu-hash64.h
@@ -262,6 +262,7 @@ extern void slb_initialize(void);
 extern void slb_flush_and_rebolt(void);
 extern void stab_initialize(unsigned long stab);
 
+extern void slb_vmalloc_update(void);
 #endif /* __ASSEMBLY__ */
 
 /*