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

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Date:	Thu, 4 Dec 2014 12:03:05 +0000
From:	Catalin Marinas <catalin.marinas@....com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	"Wang, Yalin" <Yalin.Wang@...ymobile.com>,
	"'linux-mm@...ck.org'" <linux-mm@...ck.org>,
	Will Deacon <Will.Deacon@....com>,
	"'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 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.

-- 
Catalin
--
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