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

From: Peter Maydell
Subject: Re: [Qemu-devel] [PATCH 2.4] hw/arm/boot: Increase fdt alignment
Date: Mon, 13 Jul 2015 17:13:46 +0100

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:

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

-- PMM

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