This is a note to let you know that I've just added the patch titled
ARM: 7767/1: let the ASID allocator handle suspended animation
to the 3.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
arm-7767-1-let-the-asid-allocator-handle-suspended-animation.patch
and it can be found in the queue-3.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From ae120d9edfe96628f03d87634acda0bfa7110632 Mon Sep 17 00:00:00 2001
From: Marc Zyngier <Marc.Zyngier@xxxxxxx>
Date: Fri, 21 Jun 2013 12:06:19 +0100
Subject: ARM: 7767/1: let the ASID allocator handle suspended animation
From: Marc Zyngier <Marc.Zyngier@xxxxxxx>
commit ae120d9edfe96628f03d87634acda0bfa7110632 upstream.
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 = <x 0>]
[suspended] runs B{y} [active = <x y>]
[rollover:
active = <0 0>
reserved = <x y>]
runs B{y} [active = <0 y>
reserved = <x y>]
[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.
Acked-by: Will Deacon <will.deacon@xxxxxxx>
Acked-by: Catalin Carinas <catalin.marinas@xxxxxxx>
Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx>
Signed-off-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/arm/mm/context.c | 9 +++++++++
1 file changed, 9 insertions(+)
--- a/arch/arm/mm/context.c
+++ b/arch/arm/mm/context.c
@@ -128,6 +128,15 @@ static void flush_context(unsigned int c
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;
Patches currently in stable-queue which might be from Marc.Zyngier@xxxxxxx are
queue-3.10/arm-7767-1-let-the-asid-allocator-handle-suspended-animation.patch
queue-3.10/arm-7768-1-prevent-risks-of-out-of-bound-access-in-asid-allocator.patch
queue-3.10/arm-7769-1-cortex-a15-fix-erratum-798181-implementation.patch
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