[PATCH] Fix non-LPAE boot regression.

On Monday 15 August 2011 15:09:14 Catalin Marinas wrote:

Hi Vasily,

On Sat, Aug 13, 2011 at 01:58:19PM +0100, Vasily Khoruzhick wrote:

quoted

It was introduced by  407f8b4cb07cbc5c1c7cc386f231224e2524ccea
ARM: LPAE: MMU setup for the 3-level page table format

Signed-off-by: Vasily Khoruzhick <anarsoul@gmail.com>
---

 arch/arm/kernel/head.S |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm/kernel/head.S b/arch/arm/kernel/head.S
index 0bdafc4..5add5f5 100644
--- a/arch/arm/kernel/head.S
+++ b/arch/arm/kernel/head.S

@@ -206,7 +206,7 @@ __create_page_tables:
 1:	orr	r3, r7, r5, lsl #SECTION_SHIFT	@ flags + kernel base
 
 	str	r3, [r4, r5, lsl #PMD_ORDER]	@ identity mapping
 	cmp	r5, r6

-	addlo	r5, r5, #SECTION_SHIFT >> 20	@ next section
+	addlo	r5, r5, #1			@ next section

 	blo	1b

That's correct.

quoted

 	/*

@@ -217,7 +217,7 @@ __create_page_tables:
 	mov	r3, r3, lsr #SECTION_SHIFT
 	orr	r3, r7, r3, lsl #SECTION_SHIFT
 	add	r0, r4,  #(KERNEL_START & 0xff000000) >> (SECTION_SHIFT -
 	PMD_ORDER)

-	str	r3, [r0, #(KERNEL_START & 0x00e00000) >> (SECTION_SHIFT -

PMD_ORDER)]! +	str	r3, [r0, #(KERNEL_START & 0x00f00000) >>
(SECTION_SHIFT - PMD_ORDER)]!

The reason for this was that the sections are 2MB with LPAE and a page
table entry is 64-bit wide. We always shift that value by 18 but with
LPAE we don't want to write in the middle of a page table entry if
KERNEL_START is not 2MB aligned.

But if KERNEL_START is not 2MB aligned, I think we get the wrong
physical address by 1MB (with the classic page table format).

Yep, for my case KERNEL_START is not 2MB aligned (TEXT_OFFSET is 0x00108000). 
(CONFIG_PM_H1940 is set)

There are a few alternatives to fixing this:

1. Different KERNEL_START masking for classic or LPAE page tables.
2. Always force 2MB section and the code above moving the phys addr into
   r3 would need to take this into account.

I would go for 1 with some shifting like below:

+	str	r3, [r0, #((KERNEL_START & 0x00f00000) >> SECTION_SHIFT) <<
PMD_ORDER]!

This should give us 0x00f00000 with classic page tables and 0x00e00000
with LPAE.

Thanks.

Ok, I'll test this change when I get home.

Regards
Vasily