Re: [Qemu-devel] Re: [PATCH 2 of 5] add can_dma/post_dma for direct IO

Thiemo Seufer
2008-12-23T00:03:39Z

Avi Kivity wrote:
> Ian Jackson wrote:
>> Avi Kivity writes ("[Qemu-devel] Re: [PATCH 2 of 5] add can_dma/post_dma for direct IO"):
>>
>>> Newer Xen shouldn't have this problem though; it runs qemu in kernel
>>> mode in a dedicated 64-bit domain.
>>>
>>
>> I think there is continued value in being able to emulate a guest
>> whose physical address space exceeds the virtual address space in the
>> host. The whole assumption that all guest accessible RAM is mapped at
>> once, contiguously, is I think wrong.
>>
>
> I agree that we shouldn't expect memory to be contiguous, in order to
> properly support hotplug. But I see zero value in trying to support
> large memory configurations on 32-bit in 2008. This is what 64-bit
> systems are for! If Xen has a problem with 64-bit hosts, we can try to
> accommodate it, but to have 32-bit qemu/tcg

Running x86-64 binaries on a (non-x86) 32-bit host is IMHO quite an
obvious application for qemu/tcg.

> or qemu/kvm support large address spaces is pointless IMO.

Interestingly, Virtualbox just started to support
64-bit-target-on-32-bit-host.

Thiemo