ARM: btc: avoid invalidating the branch target cache on kernel TLB maintanence

Kernel space needs very little in the way of BTC maintanence as most
mappings which are created and destroyed are non-executable, and so
could never enter the instruction stream.

The case which does warrant BTC maintanence is when a module is loaded.
This creates a new executable mapping, but at that point the pages have
not been initialized with code and data, so at that point they contain
unpredictable information.  Invalidating the BTC at this stage serves
little useful purpose.

Before we execute module code, we call flush_icache_range(), which deals
with the BTC maintanence requirements.  This ensures that we have a BTC
maintanence operation before we execute code via the newly created
mapping.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/include/asm/tlbflush.h

@@ -34,16 +34,12 @@
 #define TLB_V6_D_ASID	(1 << 17)
 #define TLB_V6_I_ASID	(1 << 18)
 
-#define TLB_BTB		(1 << 28)
-
 /* Unified Inner Shareable TLB operations (ARMv7 MP extensions) */
 #define TLB_V7_UIS_PAGE	(1 << 19)
 #define TLB_V7_UIS_FULL (1 << 20)
 #define TLB_V7_UIS_ASID (1 << 21)
 
-/* Inner Shareable BTB operation (ARMv7 MP extensions) */
-#define TLB_V7_IS_BTB	(1 << 22)
-
+#define TLB_BARRIER	(1 << 28)
 #define TLB_L2CLEAN_FR	(1 << 29)		/* Feroceon */
 #define TLB_DCLEAN	(1 << 30)
 #define TLB_WB		(1 << 31)
@@ -58,7 +54,7 @@
  *	  v4wb  - ARMv4 with write buffer without I TLB flush entry instruction
  *	  v4wbi - ARMv4 with write buffer with I TLB flush entry instruction
  *	  fr    - Feroceon (v4wbi with non-outer-cacheable page table walks)
- *	  fa    - Faraday (v4 with write buffer with UTLB and branch target buffer (BTB))
+ *	  fa    - Faraday (v4 with write buffer with UTLB)
  *	  v6wbi - ARMv6 with write buffer with I TLB flush entry instruction
  *	  v7wbi - identical to v6wbi
  */
@@ -99,7 +95,7 @@
 # define v4_always_flags	(-1UL)
 #endif
 
-#define fa_tlb_flags	(TLB_WB | TLB_BTB | TLB_DCLEAN | \
+#define fa_tlb_flags	(TLB_WB | TLB_DCLEAN | TLB_BARRIER | \
 			 TLB_V4_U_FULL | TLB_V4_U_PAGE)
 
 #ifdef CONFIG_CPU_TLB_FA
@@ -166,7 +162,7 @@
 # define v4wb_always_flags	(-1UL)
 #endif
 
-#define v6wbi_tlb_flags (TLB_WB | TLB_DCLEAN | TLB_BTB | \
+#define v6wbi_tlb_flags (TLB_WB | TLB_DCLEAN | TLB_BARRIER | \
 			 TLB_V6_I_FULL | TLB_V6_D_FULL | \
 			 TLB_V6_I_PAGE | TLB_V6_D_PAGE | \
 			 TLB_V6_I_ASID | TLB_V6_D_ASID)
@@ -184,9 +180,9 @@
 # define v6wbi_always_flags	(-1UL)
 #endif
 
-#define v7wbi_tlb_flags_smp	(TLB_WB | TLB_DCLEAN | TLB_V7_IS_BTB | \
+#define v7wbi_tlb_flags_smp	(TLB_WB | TLB_DCLEAN | TLB_BARRIER | \
 			 TLB_V7_UIS_FULL | TLB_V7_UIS_PAGE | TLB_V7_UIS_ASID)
-#define v7wbi_tlb_flags_up	(TLB_WB | TLB_DCLEAN | TLB_BTB | \
+#define v7wbi_tlb_flags_up	(TLB_WB | TLB_DCLEAN | TLB_BARRIER | \
 			 TLB_V6_U_FULL | TLB_V6_U_PAGE | TLB_V6_U_ASID)
 
 #ifdef CONFIG_CPU_TLB_V7
@@ -341,15 +337,7 @@ static inline void local_flush_tlb_all(void)
 	if (tlb_flag(TLB_V7_UIS_FULL))
 		asm("mcr p15, 0, %0, c8, c3, 0" : : "r" (zero) : "cc");
 
-	if (tlb_flag(TLB_BTB)) {
-		/* flush the branch target cache */
-		asm("mcr p15, 0, %0, c7, c5, 6" : : "r" (zero) : "cc");
-		dsb();
-		isb();
-	}
-	if (tlb_flag(TLB_V7_IS_BTB)) {
-		/* flush the branch target cache */
-		asm("mcr p15, 0, %0, c7, c1, 6" : : "r" (zero) : "cc");
+	if (tlb_flag(TLB_BARRIER)) {
 		dsb();
 		isb();
 	}
@@ -389,17 +377,8 @@ static inline void local_flush_tlb_mm(struct mm_struct *mm)
 		asm("mcr p15, 0, %0, c8, c3, 2" : : "r" (asid) : "cc");
 #endif
 
-	if (tlb_flag(TLB_BTB)) {
-		/* flush the branch target cache */
-		asm("mcr p15, 0, %0, c7, c5, 6" : : "r" (zero) : "cc");
-		dsb();
-	}
-	if (tlb_flag(TLB_V7_IS_BTB)) {
-		/* flush the branch target cache */
-		asm("mcr p15, 0, %0, c7, c1, 6" : : "r" (zero) : "cc");
+	if (tlb_flag(TLB_BARRIER))
 		dsb();
-		isb();
-	}
 }
 
 static inline void
@@ -439,17 +418,8 @@ local_flush_tlb_page(struct vm_area_struct *vma, unsigned long uaddr)
 		asm("mcr p15, 0, %0, c8, c3, 1" : : "r" (uaddr) : "cc");
 #endif
 
-	if (tlb_flag(TLB_BTB)) {
-		/* flush the branch target cache */
-		asm("mcr p15, 0, %0, c7, c5, 6" : : "r" (zero) : "cc");
-		dsb();
-	}
-	if (tlb_flag(TLB_V7_IS_BTB)) {
-		/* flush the branch target cache */
-		asm("mcr p15, 0, %0, c7, c1, 6" : : "r" (zero) : "cc");
+	if (tlb_flag(TLB_BARRIER))
 		dsb();
-		isb();
-	}
 }
 
 static inline void local_flush_tlb_kernel_page(unsigned long kaddr)
@@ -482,15 +452,7 @@ static inline void local_flush_tlb_kernel_page(unsigned long kaddr)
 	if (tlb_flag(TLB_V7_UIS_PAGE))
 		asm("mcr p15, 0, %0, c8, c3, 1" : : "r" (kaddr) : "cc");
 
-	if (tlb_flag(TLB_BTB)) {
-		/* flush the branch target cache */
-		asm("mcr p15, 0, %0, c7, c5, 6" : : "r" (zero) : "cc");
-		dsb();
-		isb();
-	}
-	if (tlb_flag(TLB_V7_IS_BTB)) {
-		/* flush the branch target cache */
-		asm("mcr p15, 0, %0, c7, c1, 6" : : "r" (zero) : "cc");
+	if (tlb_flag(TLB_BARRIER)) {
 		dsb();
 		isb();
 	}

arch/arm/mm/tlb-fa.S

@@ -46,7 +46,6 @@ ENTRY(fa_flush_user_tlb_range)
 	add	r0, r0, #PAGE_SZ
 	cmp	r0, r1
 	blo	1b
-	mcr	p15, 0, r3, c7, c5, 6		@ invalidate BTB
 	mcr	p15, 0, r3, c7, c10, 4		@ data write barrier
 	mov	pc, lr
 
@@ -60,9 +59,8 @@ ENTRY(fa_flush_kern_tlb_range)
 	add	r0, r0, #PAGE_SZ
 	cmp	r0, r1
 	blo	1b
-	mcr	p15, 0, r3, c7, c5, 6		@ invalidate BTB
 	mcr	p15, 0, r3, c7, c10, 4		@ data write barrier
-	mcr	p15, 0, r3, c7, c5, 4		@ prefetch flush
+	mcr	p15, 0, r3, c7, c5, 4		@ prefetch flush (isb)
 	mov	pc, lr
 
 	__INITDATA

arch/arm/mm/tlb-v6.S

@@ -54,7 +54,6 @@ ENTRY(v6wbi_flush_user_tlb_range)
 	add	r0, r0, #PAGE_SZ
 	cmp	r0, r1
 	blo	1b
-	mcr	p15, 0, ip, c7, c5, 6		@ flush BTAC/BTB
 	mcr	p15, 0, ip, c7, c10, 4		@ data synchronization barrier
 	mov	pc, lr
 
@@ -83,9 +82,8 @@ ENTRY(v6wbi_flush_kern_tlb_range)
 	add	r0, r0, #PAGE_SZ
 	cmp	r0, r1
 	blo	1b
-	mcr	p15, 0, r2, c7, c5, 6		@ flush BTAC/BTB
 	mcr	p15, 0, r2, c7, c10, 4		@ data synchronization barrier
-	mcr	p15, 0, r2, c7, c5, 4		@ prefetch flush
+	mcr	p15, 0, r2, c7, c5, 4		@ prefetch flush (isb)
 	mov	pc, lr
 
 	__INIT

arch/arm/mm/tlb-v7.S

@@ -48,9 +48,6 @@ ENTRY(v7wbi_flush_user_tlb_range)
 	add	r0, r0, #PAGE_SZ
 	cmp	r0, r1
 	blo	1b
-	mov	ip, #0
-	ALT_SMP(mcr	p15, 0, ip, c7, c1, 6)	@ flush BTAC/BTB Inner Shareable
-	ALT_UP(mcr	p15, 0, ip, c7, c5, 6)	@ flush BTAC/BTB
 	dsb
 	mov	pc, lr
 ENDPROC(v7wbi_flush_user_tlb_range)
@@ -75,9 +72,6 @@ ENTRY(v7wbi_flush_kern_tlb_range)
 	add	r0, r0, #PAGE_SZ
 	cmp	r0, r1
 	blo	1b
-	mov	r2, #0
-	ALT_SMP(mcr	p15, 0, r2, c7, c1, 6)	@ flush BTAC/BTB Inner Shareable
-	ALT_UP(mcr	p15, 0, r2, c7, c5, 6)	@ flush BTAC/BTB
 	dsb
 	isb
 	mov	pc, lr