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    SubjectRe: [PATCH] Fix non-LPAE boot regression.
    Hi Vasily,

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

    > /*
    > @@ -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).

    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.

    --
    Catalin


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