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-rw-r--r--arch/arm/mm/context.c16
1 files changed, 10 insertions, 6 deletions
diff --git a/arch/arm/mm/context.c b/arch/arm/mm/context.c
index 52e6f13ac9c7..6eb97b3a7481 100644
--- a/arch/arm/mm/context.c
+++ b/arch/arm/mm/context.c
@@ -36,8 +36,8 @@
* The context ID is used by debuggers and trace logic, and
* should be unique within all running processes.
*
- * In big endian operation, the two 32 bit words are swapped if accesed by
- * non 64-bit operations.
+ * In big endian operation, the two 32 bit words are swapped if accessed
+ * by non-64-bit operations.
*/
#define ASID_FIRST_VERSION (1ULL << ASID_BITS)
#define NUM_USER_ASIDS ASID_FIRST_VERSION
@@ -195,8 +195,11 @@ static u64 new_context(struct mm_struct *mm, unsigned int cpu)
* Allocate a free ASID. If we can't find one, take a
* note of the currently active ASIDs and mark the TLBs
* as requiring flushes. We always count from ASID #1,
- * as we reserve ASID #0 to switch via TTBR0 and indicate
- * rollover events.
+ * as we reserve ASID #0 to switch via TTBR0 and to
+ * avoid speculative page table walks from hitting in
+ * any partial walk caches, which could be populated
+ * from overlapping level-1 descriptors used to map both
+ * the module area and the userspace stack.
*/
asid = find_next_zero_bit(asid_map, NUM_USER_ASIDS, cur_idx);
if (asid == NUM_USER_ASIDS) {
@@ -224,8 +227,9 @@ void check_and_switch_context(struct mm_struct *mm, struct task_struct *tsk)
__check_vmalloc_seq(mm);
/*
- * Required during context switch to avoid speculative page table
- * walking with the wrong TTBR.
+ * We cannot update the pgd and the ASID atomicly with classic
+ * MMU, so switch exclusively to global mappings to avoid
+ * speculative page table walking with the wrong TTBR.
*/
cpu_set_reserved_ttbr0();