ARM: mm: remove IPI broadcasting on ASID rollover

ASIDs are allocated to MMU contexts based on a rolling counter. This
means that after 255 allocations we must invalidate all existing ASIDs
via an expensive IPI mechanism to synchronise all of the online CPUs and
ensure that all tasks execute with an ASID from the new generation.

This patch changes the rollover behaviour so that we rely instead on the
hardware broadcasting of the TLB invalidation to avoid the IPI calls.
This works by keeping track of the active ASID on each core, which is
then reserved in the case of a rollover so that currently scheduled
tasks can continue to run. For cores without hardware TLB broadcasting,
we keep track of pending flushes in a cpumask, so cores can flush their
local TLB before scheduling a new mm.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Tested-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

1 files changed, 4 insertions, 7 deletions

diff --git a/arch/arm/include/asm/mmu.h b/arch/arm/include/asm/mmu.h
index 14965658a923..5b53b53ab5cf 100644
--- a/arch/arm/include/asm/mmu.h
+++ b/arch/arm/include/asm/mmu.h
@@ -5,18 +5,15 @@
 
 typedef struct {
 #ifdef CONFIG_CPU_HAS_ASID
-        unsigned int id;
-        raw_spinlock_t id_lock;
+        u64 id;
 #endif
         unsigned int kvm_seq;
 } mm_context_t;
 
 #ifdef CONFIG_CPU_HAS_ASID
-#define ASID(mm)        ((mm)->context.id & 255)
-
-/* init_mm.context.id_lock should be initialized. */
-#define INIT_MM_CONTEXT(name)                                                 \
-        .context.id_lock    = __RAW_SPIN_LOCK_UNLOCKED(name.context.id_lock),
+#define ASID_BITS       8
+#define ASID_MASK       ((~0ULL) << ASID_BITS)
+#define ASID(mm)        ((mm)->context.id & ~ASID_MASK)
 #else
 #define ASID(mm)        (0)
 #endif