Re: [Xen-devel] Enable virtual memory for Mini-os on ARM

["karim.allah.ahmed@xxxxxxxxx" <karim.allah.ahmed@xxxxxxxxx>]

On Mon, Dec 23, 2013 at 10:38 AM, Samuel Thibault <samuel.thibault@xxxxxxxxxxxx> wrote:

karim.allah.ahmed@xxxxxxxxx, le Mon 23 Dec 2013 10:23:01 +0000, a écrit :

> Why do I need to create pagetables and fill them for mini-os ?

I don't know the virtual memory of ARM, but on x86 we definitely need a
pagetable because very often we need to map/unmap things, like granted
mfns, i/o areas, foreign pages, etc.

Can you please refer me to the part of the code related to any of these cases ?

 

In ARM MMU is virtualized in HW. So you've an extra level of translation that's controlled by the hypervisor.

So, Is there a reason for doing map/unmap on virtual address space not on physical one ?

For me I would use virtual memory for:

1- Isolation between different entities ( processes ) - ( Is that applicable to mini-os ? I can see that things like fork isn't supported by mini-os [unsupported_function_crash(fork);], which makes me think that this isn't applicable )

2- creating a contiguous mapping of scattered pages.

Are any of these a concern at the moment ?

Thanks.

Samuel

--

Karim Allah Ahmed.

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