Re: [Xen-devel] XEN[ARM] Master not working on Allwinner A20

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Sun, 2014-01-05 at 16:48 +0000, karim.allah.ahmed@xxxxxxxxx wrote:

> If you still can't boot with any memory bigger than 128M, as a fast
> workaround you can apply this patch.

I wonder if it might be possible to work around this by more carefully
selecting the load addresses for Xen+Linux+DTB+initrd, such that they
are packed into the top end of RAM, leaving a larger contiguous chunk
available at the beginning. e.g. if sizeof(Xen)=X and sizeof(Linux)=L
and sizeof(DTB)=D (all rounded up to 2M boundary) then load things at:
        MEMMAX-X:       Leave free for high relocation of hypervisor
        MEMMAX-X-L:     Load Linux here
        MEMMAX-X-L-D:   Load DTB here
        MEMMAX-X-L-D-X: Load initial Xen image here

Ultimately this is because allocations need to be aligned to their size,
so on a 1GB system there are only two possible 512MB allocations, if
even one page is allocated in each half then it isn't possible to
satisfy things. I don't think the core allocator gives us the option to
do non-aligned allocations. Disabling the 1:1 mapping workaround
allocates the region a page at a time so it doesn't suffer from this.

We are probably mostly stuck with this for 4.4. As Julien says for 4.5
we should probably look into giving dom0 multiple banks where necessary.

Ian.



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