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 12:05:06 +0000
From:	Will Deacon <will.deacon@....com>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	"Wang, Yalin" <Yalin.Wang@...ymobile.com>,
	"'linux-mm@...ck.org'" <linux-mm@...ck.org>,
	"'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>,
	"'linux-arm-kernel@...ts.infradead.org'" 
	<linux-arm-kernel@...ts.infradead.org>,
	"'linux-arm-msm@...r.kernel.org'" <linux-arm-msm@...r.kernel.org>,
	Peter Maydell <Peter.Maydell@....com>
Subject: Re: [RFC v2] arm:extend the reserved mrmory for initrd to be page
 aligned

On Thu, Dec 04, 2014 at 12:03:05PM +0000, Catalin Marinas wrote:
> On Mon, Sep 15, 2014 at 12:33:25PM +0100, Russell King - ARM Linux wrote:
> > On Mon, Sep 15, 2014 at 07:07:20PM +0800, Wang, Yalin wrote:
> > > @@ -636,6 +646,11 @@ static int keep_initrd;
> > >  void free_initrd_mem(unsigned long start, unsigned long end)
> > >  {
> > >  	if (!keep_initrd) {
> > > +		if (start == initrd_start)
> > > +			start = round_down(start, PAGE_SIZE);
> > > +		if (end == initrd_end)
> > > +			end = round_up(end, PAGE_SIZE);
> > > +
> > >  		poison_init_mem((void *)start, PAGE_ALIGN(end) - start);
> > >  		free_reserved_area((void *)start, (void *)end, -1, "initrd");
> > >  	}
> > 
> > is the only bit of code you likely need to achieve your goal.
> > 
> > Thinking about this, I think that you are quite right to align these.
> > The memory around the initrd is defined to be system memory, and we
> > already free the pages around it, so it *is* wrong not to free the
> > partial initrd pages.
> 
> Actually, I think we have a problem, at least on arm64 (raised by Peter
> Maydell). There is no guarantee that the page around start/end of initrd
> is free, it may contain the dtb for example. This is even more obvious
> when we have a 64KB page kernel (the boot loader doesn't know the page
> size that the kernel is going to use).
> 
> The bug was there before as we had poison_init_mem() already (not it
> disappeared since free_reserved_area does the poisoning).
> 
> So as a quick fix I think we need the rounding the other way (and in the
> general case we probably lose a page at the end of initrd):
> 
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index 494297c698ca..39fd080683e7 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -335,9 +335,9 @@ void free_initrd_mem(unsigned long start, unsigned long end)
>  {
>  	if (!keep_initrd) {
>  		if (start == initrd_start)
> -			start = round_down(start, PAGE_SIZE);
> +			start = round_up(start, PAGE_SIZE);
>  		if (end == initrd_end)
> -			end = round_up(end, PAGE_SIZE);
> +			end = round_down(end, PAGE_SIZE);
>  
>  		free_reserved_area((void *)start, (void *)end, 0, "initrd");
>  	}
> 
> A better fix would be to check what else is around the start/end of
> initrd.

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.

Will
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