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Re: [Xen-devel] [PATCH 0/2] xen: Switch to virtual mapped linear p2m list

On 10/27/2014 04:16 PM, David Vrabel wrote:
On 27/10/14 14:52, Juergen Gross wrote:
Paravirtualized kernels running on Xen use a three level tree for
translation of guest specific physical addresses to machine global
addresses. This p2m tree is used for construction of page table
entries, so the p2m tree walk is performance critical.

By using a linear virtual mapped p2m list accesses to p2m elements
can be sped up while even simplifying code. To achieve this goal
some p2m related initializations have to be performed later in the
boot process, as the final p2m list can be set up only after basic
memory management functions are available.

What impact does this have on 32-bit guests which don't have huge amount
of virtual address space?

I think a 32-bit guest could have up to 64 GiB of PFNs, which would
require a 128 MiB p2m array, which is too large?

It is 64 MB (one entry on 32 bit is 32 bits :-) ).

With a m2p array of only 16 MB size I doubt a 32 bit guest can be larger
than 16 GB, or am I wrong here?


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