Re: [Xen-devel] [PATCH] xen/arm: Allocate memory for dom0 from the bottom with the 1:1 Workaround

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Tue, 2013-10-22 at 14:58 +0100, Julien Grall wrote:
> On 22 October 2013 12:26, Ian Campbell <ian.campbell@xxxxxxxxxx> wrote:
> > On Tue, 2013-10-22 at 11:51 +0100, Julien Grall wrote:
> >> On Linux, the option CONFIG_ARM_PATCH_PHYS_VIRT (by default enabled) allows
> >> the Kernel to be loaded anywhere (or nearly) by patching the translation
> >> pv<->virt at boot time.
> >>
> >> The current solution in Linux assuming that the delta physical address -
> >> virtual address is always negative. A positive delta will destroy all the
> >> optimisation to modify only a part of the translation instruction 
> >> (add/sub).
> >>
> >> By default, Xen is allocating memory from the top of memory and then
> >> goes down. To avoid booting issue with Linux, we must allocate memory
> >> from the bottom (ie starting from 0).
> >>
> >> Signed-off-by: Julien Grall <julien.grall@xxxxxxxxxx>
> >
> > Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
> >
> > OOI how low does the memory get allocated in practice? We deliberately
> > load Xen and place xenheap up high so I guess for dom0 we can't get
> > memory from pretty low down?
> 
> It depends where U-boot has loaded the different modules (kernel,
> initrd, device tree,...).
> If they are not loaded at the bottom of the RAM, Xen is able to use
> the first address of the first bank.

Great! That's what I was hoping.

Thanks,
Ian.




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