[ARM] Fix ASID version switch

Close a hole in the ASID version switch, particularly the following
scenario:

CPU0 MM PID			CPU1 MM PID
	idle
				  A	pid(A)
				  A	idle(lazy tlb)
		* new asid version triggered by B *
  B	pid(B)
  A	pid(A)
		* MM A gets new asid version *
  A	idle(lazy tlb)
				  A	pid(A)
		* CPU1 doesn't see the new ASID *

The result is that CPU1 continues running with the hardware set
for the original (stale) ASID value, but mm->context.id contains
the new ASID value.  The result is that the next MM fault on CPU1
updates the page table entries, but flush_tlb_page() fails due to
wrong ASID.

There is a related case with a threaded application is allocated
a new ASID on one CPU while another of its threads is running on
some different CPU.  This scenario is not fixed by this commit.

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

1 files changed, 4 insertions, 4 deletions

diff --git a/include/asm-arm/mmu_context.h b/include/asm-arm/mmu_context.h
index f8755c818b5..4981ad41919 100644
--- a/include/asm-arm/mmu_context.h
+++ b/include/asm-arm/mmu_context.h
@@ -36,8 +36,9 @@ void __check_kvm_seq(struct mm_struct *mm);
  * The context ID is used by debuggers and trace logic, and
  * should be unique within all running processes.
  */
-#define ASID_BITS	8
-#define ASID_MASK	((~0) << ASID_BITS)
+#define ASID_BITS		8
+#define ASID_MASK		((~0) << ASID_BITS)
+#define ASID_FIRST_VERSION	(1 << ASID_BITS)
 
 extern unsigned int cpu_last_asid;
 
@@ -96,8 +97,7 @@ switch_mm(struct mm_struct *prev, struct mm_struct *next,
 #ifdef CONFIG_MMU
 	unsigned int cpu = smp_processor_id();
 
-	if (prev != next) {
-		cpu_set(cpu, next->cpu_vm_mask);
+	if (!cpu_test_and_set(cpu, next->cpu_vm_mask) || prev != next) {
 		check_context(next);
 		cpu_switch_mm(next->pgd, next);
 		if (cache_is_vivt())