Re: [Xen-devel] [PATCH 4/5] xen: arm: avoid unnecessary aliasing in boot page tables.

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2014-07-14 at 17:39 +0100, Ian Campbell wrote:
> If the identity map is created at one level then avoid creating
> entries further down the boot page tables, since these will be aliases
> at strange virtual address

Julien asked me what this meant IRL but it's easier to explain with an
written example I think.

Consider an arm32 system (for simplicity) with Xen loaded at address
0x40402000. As a virtual address this corresponds to walking offsets 1,
2 and 2 at the first, second and third levels respectively.

When creating the identity map we will therefore create a 1GB super
mapping at 0x40000000 for the identity map, which is the one we want to
use.

However when considering the second level we will see the offset 2 and
create a 2MB mapping in slot 2 of boot_second. Since boot_second is
mapped in slot 0 of boot_first this corresponds to an unwanted mapping
from virtual address 0x00400000 to physical address 0x40400000.

Hope that clears things up.

Ian.


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel