Re: [Qemu-devel] [PATCH 2.4] hw/arm/boot: Increase fdt alignment

[Peter Maydell]

On 13 July 2015 at 16:56, Alexander Graf <address@hidden> wrote:
> The Linux kernel on aarch64 creates a page table entry at early bootup
> that spans the 2MB range on memory spanning the fdt start address:
>
>   [ ALIGN_DOWN(fdt, 2MB) ... ALIGN_DOWN(fdt, 2MB) + 2MB ]
>
> This means that when our current 4k alignment happens to fall at the end
> of the aligned region, Linux tries to access memory that is not mapped.
>
> The easy fix is to instead increase the alignment to 2MB, making Linux's
> logic always succeed.

This is a kernel bug and should be fixed there. The booting
protocol document is pretty clear:
https://www.kernel.org/doc/Documentation/arm64/booting.txt

"The device tree blob (dtb) must be placed on an 8-byte boundary"

-- PMM