linux-kernel - Re: [PATCH v2] arm64: Add support for new control bits CTR_EL0.DIC and CTR

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Message-ID: <20180221131203.GB7614@arm.com>
Date:   Wed, 21 Feb 2018 13:12:04 +0000
From:   Will Deacon <will.deacon@....com>
To:     Shanker Donthineni <shankerd@...eaurora.org>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Thomas Speier <tspeier@...eaurora.org>,
        Vikram Sethi <vikrams@...eaurora.org>,
        Marc Zyngier <marc.zyngier@....com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Philip Elcan <pelcan@...eaurora.org>,
        kvmarm <kvmarm@...ts.cs.columbia.edu>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2] arm64: Add support for new control bits CTR_EL0.DIC
 and CTR_EL0.IDC

On Wed, Feb 21, 2018 at 07:10:34AM -0600, Shanker Donthineni wrote:
> On 02/21/2018 05:12 AM, Catalin Marinas wrote:
> > However, my worry is that in an implementation with DIC set, we also
> > skip the DSB/ISB sequence in the invalidate_icache_by_line macro. For
> > example, in an implementation with transparent PoU, we could have:
> > 
> > 	str	<some instr>, [addr]
> > 	// no cache maintenance or barrier
> > 	br	<addr>
> > 
> 
> Thanks for pointing out the missing barriers. I think it make sense to follow
> the existing barrier semantics in order to avoid the unknown things.
>  
> > Is an ISB required between the instruction store and execution? I would
> > say yes but maybe Will has a better opinion here.
> > 
> Agree, an ISB is required especially for self-modifying code. I'll include in v3 patch. 

I'd have thought you'd need a DSB too, before the ISB.

Will