[Xen-users] Question on pseudo-physical memory

[mjfeeney@xxxxxxxxxxx]

Hello,
 
I was reading the Xen 3.0 Interface Guide and there was a statement that concerned me.  Specifically:
 
"Pseudo-physical memory, on the other hand, is a per-domain abstraction. It allows a guest operating system to consider its memory allocation to consist of a contiguous range of physical page frames starting at physical frame 0, despite the fact that the underlying machine page frames may be sparsely allocated and in any order."
 
Does this mean that a Domain0 Linux kernel driver which allocated kernel memory with kmalloc() or __get_free_pages() may not receive memory that is physically contiguous in the underlying real memory?  I ask because this could cause an issue for a device driver that must build scatter/gather lists for an external device.  If this is true, is there documentation available on what's required to build a valid scatter/gather list which contains real physically contiguous segments?
 
Thanks - Martin

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