[PATCH RT] arm*: disable NEON in kernel mode
From: peterz@infradead.org (Peter Zijlstra)
Date: 2017-12-01 17:15:13
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linux-rt-users, lkml
On Fri, Dec 01, 2017 at 03:36:48PM +0100, Sebastian Andrzej Siewior wrote:
On 2017-12-01 14:18:28 [+0000], Mark Rutland wrote:quoted
[Adding Ard, who wrote the NEON crypto code] On Fri, Dec 01, 2017 at 02:45:06PM +0100, Sebastian Andrzej Siewior wrote:quoted
+arm folks, to let you know On 2017-12-01 11:43:32 [+0100], To linux-rt-users at vger.kernel.org wrote:quoted
NEON in kernel mode is used by the crypto algorithms and raid6 code. While the raid6 code looks okay, the crypto algorithms do not: NEON is enabled on first invocation and may allocate/free/map memory before the NEON mode is disabled again.Could you elaborate on why this is a problem? I guess this is because kernel_neon_{begin,end}() disable preemption? ... is this specific to RT?It is RT specific, yes. One thing are the unbounded latencies since everything in this preempt_disable section can take time depending on the size of the request.
Well, PREEMPT cares about that too.