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Re: [Xen-devel] [RFC] xen/arm: Find automatically the gnttab region for DOM0


On 22/05/2015 01:38, Julien Grall wrote:
Currently, the grant table region is hardcoded per-platform. When a new
board is coming up, we have to check the spec in order to find a space
in the memory layout free. Depending on the platform it may be tedious.

A good candidate for the gnttab region is the one used by Xen binary as
some part will never be mapped to the DOM0 address, MMIO are mapped 1:1
and the RAM will be either:
     - direct mapped: 1:1 mapping is used => no problem
     - non direct mapped: Xen always relocates himself as high as possible
     (limited to 4GB on ARM32) and the RAM bank are filled from the first
     one. It's very unlikely that the gnttab region will overlap with the
     RAM. Although for safety a check may be necessary when we will reenable
     the option.

Futhermore, there is plenty of space to contain a big gnttab, the default
size is 32 frame (i.e 32KB) but it can be changed via a command option.

I miscalculate the size here. It should be 32 * 4KB = 128KB.


Julien Grall

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