Re: [Qemu-devel] [PATCH v5 10/12] hw/mips: malta: Add KVM support

Sanjay Lal
2014-06-19T19:44:28Z

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On Jun 19, 2014, at 9:27 AM, Aurelien Jarno <aurelien@aurel32.net> wrote:

> On Tue, Jun 17, 2014 at 11:10:35PM +0100, James Hogan wrote:
>> In KVM mode the bootrom is loaded and executed from the last 1MB of
>> DRAM.
>
> What is the reason for that? I am not opposed to that, but if it is
> really needed, it means that loading a bootloader into the flash area
> (for example YAMON) won't work and that this should be forbidden to the
> user.
>

In trap and emulate mode, both the kernel and userland run in user mode on the processor. Virtual addresses >= 0x80000000 are only accessible in kernel mode, and the default flash area (VA: 0xbfc00000/PA: 0x1fc00000) falls in this range.

We therefore decided to relocate the bootloader to the last 1MB of RAM. This area is excluded from the RAM ranges supplied to the kernel, so it should not be accessible to the user.

Regards
Sanjay

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