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author | Marc Zyngier <Marc.Zyngier@arm.com> | 2013-06-21 12:06:19 +0100 |
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committer | Russell King <rmk+kernel@arm.linux.org.uk> | 2013-06-24 15:24:54 +0100 |
commit | ae120d9edfe96628f03d87634acda0bfa7110632 (patch) | |
tree | 440fd50064b5745afc7613178fff7a5e5436be76 /arch/arm/mm | |
parent | 8121cf312a1908f67173ec3773da1688e04437e7 (diff) | |
download | linux-ae120d9edfe96628f03d87634acda0bfa7110632.tar.gz linux-ae120d9edfe96628f03d87634acda0bfa7110632.tar.bz2 linux-ae120d9edfe96628f03d87634acda0bfa7110632.zip |
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 = <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.
Cc: <stable@vger.kernel.org> # 3.9
Acked-by: Will Deacon <will.deacon@arm.com>
Acked-by: Catalin Carinas <catalin.marinas@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Diffstat (limited to 'arch/arm/mm')
-rw-r--r-- | arch/arm/mm/context.c | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/arch/arm/mm/context.c b/arch/arm/mm/context.c index 2ac37372ef52..8e12fcbb2c63 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; |