linux-kernel - Re: [RFC v2] arm:extend the reserved mrmory for initrd to be page aligned

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Date:	Fri, 5 Dec 2014 17:52:41 +0000
From:	Peter Maydell <peter.maydell@...aro.org>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Catalin Marinas <catalin.marinas@....com>,
	Peter Maydell <Peter.Maydell@....com>,
	"Wang, Yalin" <Yalin.Wang@...ymobile.com>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
	Will Deacon <will.deacon@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC v2] arm:extend the reserved mrmory for initrd to be page aligned

On 5 December 2014 at 17:27, Russell King - ARM Linux
<linux@....linux.org.uk> wrote:
> On Fri, Dec 05, 2014 at 05:07:45PM +0000, Catalin Marinas wrote:
>> On Fri, Dec 05, 2014 at 12:05:06PM +0000, Will Deacon wrote:
>> > Care to submit this as a proper patch? We should at least fix Peter's issue
>> > before doing things like extending headers, which won't work for older
>> > kernels anyway.
>>
>> Quick fix is the revert of the whole patch, together with removing
>> PAGE_ALIGN(end) in poison_init_mem() on arm32. If Russell is ok with
>> this patch, we can take it via the arm64 tree, otherwise I'll send you a
>> partial revert only for the arm64 part.
>
> Not really.  Let's look at the history.
>
> For years, we've been poisoning memory, page aligning the end pointer.
> This has never been an issue.

Depends what you mean by "never been an issue". I had to change
QEMU (commit 98ed805c, January 2013) for 32-bit ARM back when the
kernel started trashing the tail end of the page after the initrd
with the poisoning, to 4K-align the dtb so it didn't share a page
with the initrd-tail. That nobody else complained suggests that most
bootloaders don't in practice overlap the two, though (ie that
QEMU is an outlier in how it chooses to arrange things in memory).

I should probably have reported the breakage at the time, but
I took the pragmatic (lazy?) approach of just changing our
bootloader code.

thanks
-- PMM
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