Revert "ARM: 6943/1: mm: use TTBR1 instead of reserved context ID"

This reverts commit 52af9c6cd863fe37d1103035ec7ee22ac1296458.

Will Deacon reports that:

 In 52af9c6c ("ARM: 6943/1: mm: use TTBR1 instead of reserved context ID")
 I updated the ASID rollover code to use only the kernel page tables
 whilst updating the ASID.

 Unfortunately, the code to restore the user page tables was part of a
 later patch which isn't yet in mainline, so this leaves the code
 quite broken.

We're also in the process of eliminating __ARCH_WANT_INTERRUPTS_ON_CTXSW
from ARM, so lets revert these until we can properly sort out what we're
doing with the ARM context switching.

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

1 files changed, 5 insertions, 6 deletions

diff --git a/arch/arm/mm/context.c b/arch/arm/mm/context.c
index 8bfae964b133..b6c776ae4039 100644
--- a/arch/arm/mm/context.c
+++ b/arch/arm/mm/context.c
@@ -24,7 +24,9 @@ DEFINE_PER_CPU(struct mm_struct *, current_mm);
 
 /*
  * We fork()ed a process, and we need a new context for the child
- * to run in.
+ * to run in.  We reserve version 0 for initial tasks so we will
+ * always allocate an ASID. The ASID 0 is reserved for the TTBR
+ * register changing sequence.
  */
 void __init_new_context(struct task_struct *tsk, struct mm_struct *mm)
 {
@@ -34,11 +36,8 @@ void __init_new_context(struct task_struct *tsk, struct mm_struct *mm)
 
 static void flush_context(void)
 {
-	u32 ttb;
-	/* Copy TTBR1 into TTBR0 */
-	asm volatile("mrc	p15, 0, %0, c2, c0, 1\n"
-		     "mcr	p15, 0, %0, c2, c0, 0"
-		     : "=r" (ttb));
+	/* set the reserved ASID before flushing the TLB */
+	asm("mcr	p15, 0, %0, c13, c0, 1\n" : : "r" (0));
 	isb();
 	local_flush_tlb_all();
 	if (icache_is_vivt_asid_tagged()) {