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

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 05/12/16 16:43, Juergen Gross wrote:
> On 05/12/16 17:39, Andrew Cooper wrote:
>> 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()
> How does this help for the size of the E820 map of the physical machine
> "enhanced" by the hypervisor to reflect holes for IOAPICs and IOMMU?
>
> The problem is related to the *machine* memory map!

I clearly haven't had enough coffee yet.  I was confusing my various
machine memory maps.  Sorry for the noise.

~Andrew

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