On Fri, Dec 05, 2014 at 02:35:29AM +0000, Wang, Yalin wrote:

quoted

-----Original Message-----
From: Catalin Marinas [mailto:catalin.marinas at arm.com]
Sent: Thursday, December 04, 2014 8:03 PM
To: Russell King - ARM Linux
Cc: Wang, Yalin; 'linux-mm at kvack.org'; Will Deacon; 'linux-
kernel at vger.kernel.org'; 'linux-arm-kernel at lists.infradead.org'; 'linux-
arm-msm at vger.kernel.org'; Peter Maydell
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:

quoted

On Mon, Sep 15, 2014 at 07:07:20PM +0800, Wang, Yalin wrote:

quoted

@@ -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.

I think a better way is add some head info in Image header,
So that bootloader  can know the kernel CONFIG_PAGE_SIZE ,
For example we can add PAGE_SIZE in zImage header .
How about this way?

The problem is that we don't know how many boot loaders are affected. We
could simply mandate in booting.txt that the dtb and initrd are not
closer than 64KB but we have the same issue, existing boot loaders.

-- 
Catalin