[PATCH] ARM: 2663/1: straightify TLS register emulation a bit more

Patch from Nicolas Pitre

This better express things, and should cover RMK's weird SMP toys.

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

3 files changed, 25 insertions, 20 deletions

diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index 080df907f242..c6af1a03e081 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -505,9 +505,9 @@ ENTRY(__switch_to)
         mra     r4, r5, acc0
         stmia   ip, {r4, r5}
 #endif
-#ifdef CONFIG_HAS_TLS_REG
+#if defined(CONFIG_HAS_TLS_REG)
         mcr     p15, 0, r3, c13, c0, 3          @ set TLS register
-#else
+#elif !defined(CONFIG_TLS_REG_EMUL)
         mov     r4, #0xffff0fff
         str     r3, [r4, #-15]                  @ TLS val at 0xffff0ff0
 #endif
@@ -690,11 +690,7 @@ __kuser_cmpxchg:				@ 0xffff0fc0
 
 __kuser_get_tls:                                @ 0xffff0fe0
 
-#ifndef CONFIG_HAS_TLS_REG
-
-#ifdef CONFIG_SMP  /* sanity check */
-#error "CONFIG_SMP without CONFIG_HAS_TLS_REG is wrong"
-#endif
+#if !defined(CONFIG_HAS_TLS_REG) && !defined(CONFIG_TLS_REG_EMUL)
 
         ldr     r0, [pc, #(16 - 8)]             @ TLS stored at 0xffff0ff0
         mov     pc, lr
diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
index 8988c02119fd..14df16b983f4 100644
--- a/arch/arm/kernel/traps.c
+++ b/arch/arm/kernel/traps.c
@@ -451,9 +451,9 @@ asmlinkage int arm_syscall(int no, struct pt_regs *regs)
 
         case NR(set_tls):
                 thread->tp_value = regs->ARM_r0;
-#ifdef CONFIG_HAS_TLS_REG
+#if defined(CONFIG_HAS_TLS_REG)
                 asm ("mcr p15, 0, %0, c13, c0, 3" : : "r" (regs->ARM_r0) );
-#else
+#elif !defined(CONFIG_TLS_REG_EMUL)
                 /*
                  * User space must never try to access this directly.
                  * Expect your app to break eventually if you do so.
@@ -498,11 +498,14 @@ asmlinkage int arm_syscall(int no, struct pt_regs *regs)
         return 0;
 }
 
-#if defined(CONFIG_CPU_32v6) && !defined(CONFIG_HAS_TLS_REG)
+#ifdef CONFIG_TLS_REG_EMUL
 
 /*
  * We might be running on an ARMv6+ processor which should have the TLS
- * register, but for some reason we can't use it and have to emulate it.
+ * register but for some reason we can't use it, or maybe an SMP system
+ * using a pre-ARMv6 processor (there are apparently a few prototypes like
+ * that in existence) and therefore access to that register must be
+ * emulated.
  */
 
 static int get_tp_trap(struct pt_regs *regs, unsigned int instr)
diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig
index 27892e34b060..c4fc6be629de 100644
--- a/arch/arm/mm/Kconfig
+++ b/arch/arm/mm/Kconfig
@@ -410,17 +410,23 @@ config CPU_BPREDICT_DISABLE
         help
           Say Y here to disable branch prediction.  If unsure, say N.
 
+config TLS_REG_EMUL
+        bool
+        default y if (SMP || CPU_32v6) && (CPU_32v5 || CPU_32v4 || CPU_32v3)
+        help
+          We might be running on an ARMv6+ processor which should have the TLS
+          register but for some reason we can't use it, or maybe an SMP system
+          using a pre-ARMv6 processor (there are apparently a few prototypes
+          like that in existence) and therefore access to that register must
+          be emulated.
+
 config HAS_TLS_REG
         bool
-        depends on CPU_32v6 && !CPU_32v5 && !CPU_32v4 && !CPU_32v3
-        default y
+        depends on CPU_32v6
+        default y if !TLS_REG_EMUL
         help
           This selects support for the CP15 thread register.
-          It is defined to be available on ARMv6 or later.  However
-          if the kernel is configured to support multiple CPUs including
-          a pre-ARMv6 processors, or if a given ARMv6 processor doesn't
-          implement the thread register for some reason, then access to
-          this register from user space must be trapped and emulated.
-          If user space is relying on the __kuser_get_tls code then
-          there should not be any impact.
+          It is defined to be available on ARMv6 or later.  If a particular
+          ARMv6 or later CPU doesn't support it then it must omc;ide "select
+          TLS_REG_EMUL" along with its other caracteristics.