linux-kernel - Re: [PATCH] arm64: dts: uniphier: add /memreserve/ for spin-table release address

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Date:	Mon, 18 Apr 2016 10:04:16 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:	arm@...nel.org, devicetree@...r.kernel.org,
	Kumar Gala <galak@...eaurora.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Will Deacon <will.deacon@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] arm64: dts: uniphier: add /memreserve/ for spin-table
 release address

On Mon, Apr 18, 2016 at 05:55:14PM +0900, Masahiro Yamada wrote:
> 2016-04-18 17:45 GMT+09:00 Mark Rutland <mark.rutland@....com>:
> > I take it that the code for the spin-table is not in RAM, and does not
> > need to be protected similarly?
> 
> I use U-Boot to boot Linux for this board.
> 
> The code for the spin-table is on SDRAM, and not protected.
> 
> I already recognize this problem.
> 
> The difficulty for U-Boot is that
> U-Boot relocates itself to the top of the DRAM.
> So, it is difficult to predict
> where the code will be placed.
> 
> I will discuss this issue in the U-Boot ML.

Ok, please do.

> So, My current solution is pre-fetch the code for the spin-table onto
> I-cache.

As you are probably aware, this is incredibly unsafe, and very likely to
go wrong. Nothing guarantees that (stale) entries remain in the I-cache.

I would very much advise fixing this ASAP.

Thanks,
Mark.