Re: [Xen-devel] [PATCH 0/2] xen: modify dom0 interface for obtaining memory map

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 05/12/16 16:34, Juergen Gross wrote:
> Today's interface to get the machine memory map in dom0 requires to
> know in advance how large the final map will be. There is however no
> way to either get only a part of the memory map or to ask the
> hypervisor about its size.
>
> This patch set enhances the XENMEM_machine_memory_map hypercall to
> solve both issues by returning only a partial memory map in case the
> supplied buffer was too small and to return the needed number of
> entries if no buffer is being supplied.

These changes appear to be a good improvement in behaviour.

However, there is a way to know the exact size of the memory map.  Use
XENMEM_maximum_ram_page to find the maximum mfn, and use that to
calculate the size of the mapping.

See tools/libxc/xc_sr_common_x86_pv.c: x86_pv_map_m2p()

(Not that I think this interface is very nice either...)

~Andrew

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