* 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
* 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) {
__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();