From ae120d9edfe96628f03d87634acda0bfa7110632 Mon Sep 17 00:00:00 2001 From: Marc Zyngier Date: Fri, 21 Jun 2013 12:06:19 +0100 Subject: [PATCH] ARM: 7767/1: let the ASID allocator handle suspended animation When a CPU is running a process, the ASID for that process is held in a per-CPU variable (the "active ASIDs" array). When the ASID allocator handles a rollover, it copies the active ASIDs into a "reserved ASIDs" array to ensure that a process currently running on another CPU will continue to run unaffected. The active array is zero-ed to indicate that a rollover occurred. Because of this mechanism, a reserved ASID is only remembered for a single rollover. A subsequent rollover will completely refill the reserved ASIDs array. In a severely oversubscribed environment where a CPU can be prevented from running for extended periods of time (think virtual machines), the above has a horrible side effect: [P{a} denotes process P running with ASID a] CPU-0 CPU-1 A{x} [active = ] [suspended] runs B{y} [active = ] [rollover: active = <0 0> reserved = ] runs B{y} [active = <0 y> reserved = ] [rollover: active = <0 0> reserved = <0 y>] runs C{x} [active = <0 x>] [resumes] runs A{x} At that stage, both A and C have the same ASID, with deadly consequences. The fix is to preserve reserved ASIDs across rollovers if the CPU doesn't have an active ASID when the rollover occurs. Cc: # 3.9 Acked-by: Will Deacon Acked-by: Catalin Carinas Signed-off-by: Marc Zyngier Signed-off-by: Russell King --- arch/arm/mm/context.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/arch/arm/mm/context.c b/arch/arm/mm/context.c index 2ac3737..8e12fcb 100644 --- a/arch/arm/mm/context.c +++ b/arch/arm/mm/context.c @@ -128,6 +128,15 @@ static void flush_context(unsigned int cpu) asid = 0; } else { asid = atomic64_xchg(&per_cpu(active_asids, i), 0); + /* + * If this CPU has already been through a + * rollover, but hasn't run another task in + * the meantime, we must preserve its reserved + * ASID, as this is the only trace we have of + * the process it is still running. + */ + if (asid == 0) + asid = per_cpu(reserved_asids, i); __set_bit(ASID_TO_IDX(asid), asid_map); } per_cpu(reserved_asids, i) = asid; -- 2.7.4