Re: [Qemu-devel] 4G address space remapping on 64-bit host

[Gwenole Beauchesne]

Hi,

2007/6/29, Paul Brook <address@hidden>:
> I'd expect the overhead of SIGSEGV+mmap to be prohibitive. I don't have
> numbers to back this up, but experience with MIPS system emulation shows that
> TLB miss cost can have significant effect on overall performance.

I'd say this can't be worse than on MacOS X where Mach exception
handling is terribly slow. Typically 100 usec per fault
caught+mprotect where Linux requires less than 5 usec to do the same.

> Like Fabrice, I think this would be most useful in combination with some sort
> of hypervisor.  Somewhere on my TODO list is porting qemu to run directly as
> a paravirtual Xen DomU.  This means you can insert the guest pagetable walk
> directly into the host mmu fault handler, and do clever things with shadow
> pagetables.

This would be great. As Fabrice mentioned, the tricky part would be to
run the translator in the upper part or lower part of the 32-bit
address space. Would fixing compilation with -pie help this (with some
provisions for the dyngen ops) or do you see another means to achieve
this?
--
Gwenolé.