Re: [kvm-ppc-devel] RFC/patch portability: split kvm_vm_ioctl v2

Carsten Otte
2007-10-26T10:30:51Z

Avi Kivity wrote:
> I don't really see a big difference between what we have now (sparse
> userspace, sparse guest) and Izik's idea (contiguous userspace, sparse
> guest). In both cases you need something like memory slots to describe
> the different sections.
We don't on s390: we receive a page fault by the guest once it
accesses a sparse hole in its address space. We check the user space's
VMA and either page it in or submit an addressing exception to the guest.

> Moreover, on x86 you may want different properties for different
> sections (4K pages for the framebuffer, large pages for main memory), so
> you can't allocate memory in one big chunk.
That's right. On s390, we can live with whatever properties a section
has with regard to page size, backing device and such. So memory may
well come to live by different alloations, and different allocation
methods. All we need is a permanent contiguous mapping of the guest
physical addresses to host user addresses. So Izik's idea would work
for us even if we have different sections.