linux-kernel - Re: [PATCH v3 1/7] arm64: introduce basic aarch64 instruction decoding helpers

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Message-ID: <20131017094318.GC18765@mudshark.cambridge.arm.com>
Date:	Thu, 17 Oct 2013 10:43:19 +0100
From:	Will Deacon <will.deacon@....com>
To:	Jiang Liu <liuj97@...il.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Sandeepa Prabhu <sandeepa.prabhu@...aro.org>,
	Jiang Liu <jiang.liu@...wei.com>,
	Marc Zyngier <Marc.Zyngier@....com>,
	Arnd Bergmann <arnd@...db.de>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/7] arm64: introduce basic aarch64 instruction
 decoding helpers

On Wed, Oct 16, 2013 at 06:14:50PM +0100, Jiang Liu wrote:
> On 10/16/2013 11:36 PM, Jiang Liu wrote:
> > On 10/16/2013 06:51 PM, Will Deacon wrote:
> >> Take care here:
> >>
> >> 	- This doesn't guarantee that CPUs exclusively see new_insn (they
> >> 	  may see old_insn, even after patching)
> > Good point. Still need some synchronization mechanism lighter than
> > stop_machine(). How about kick_all_cpus_sync(), which should be lighter
> > than stop_machine()?
> For jump label, x86 uses three smp_call_function() to replace a
> stop_machine(). Seems it's valuable for us to use just one
> kick_all_cpus_sync() to avoid a stop_machine().

Yes, the exception return after handling the IPI from kick_all_cpus_sync
should be enough to synchronise the pipeline, providing that all cache
maintenance by the CPU writing the new instructions has completed (if you're
using flush_icache_range then you're fine).

Will
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