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

[Andrea Arcangeli <aarcange@redhat.com>]

On Tue, Dec 23, 2008 at 01:03:36AM +0100, Thiemo Seufer wrote:
> Running x86-64 binaries on a (non-x86) 32-bit host is IMHO quite an
> obvious application for qemu/tcg.

I doubt you need device drivers when only translating bytecode. DMA
API discussed here is an API for drivers only AFIK.

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

Yes, and KVM supports this already AFIK (without PR and without any
dynamic map/unmap operation that doesn't exist today).

The issue here is not to run 64bit target on 32bit host, this is about
running a 64bit target with >3G (or >4G of ram perhaps on sparc32 that
has separate kernel/user address space) of ram on a 32bit host.

What we're discussing here is a new feature. It's hard to imagine
any not-x86 32bit system, to want to run a >3G ram x86-64 (or any
other 64bit) VM. It wouldn't work today, and I'm not particularly
interested to make it work in 2009 and later given it's 99.9% more
likely that you have a 64bit capable CPU than >4G of ram on your
system. The limit isn't the size of the guest physical address space,
the limit is the amount of RAM that you want to give to the 64bit
guest.