Re: Paravirt KVM capabilities

Ingo Molnar
2007-01-11T00:49:57Z

* Rusty Russell <rusty-8n+1lVoiYb80n/F98K4Iww@public.gmane.org> wrote:

> > > - cr3 switches for CONFIG_PARAVIRT syscalls (which are necessary
> > > on x86_64) will probably become very cheap with tagged tlbs
> >
> > but irq overhead is nothing in importance compared to basic syscall
> > overhead. KVM/HVM already runs guest kernel syscalls at native
> > speed. KVM/LL (or Xen) has to switch cr3s to enter guest kernel
> > context
>
> Err no, this isn't true. See Documentation/lhype.txt or various blog
> entries on the subject 8) Both Xen and lhype get native syscall speeds
> (within measurement error).

i was talking about 64-bit. (we dont really design for 32-bit anymore.)
I know that lhype uses Xen's ring 1 trick, but that's a 32-bit-only
thing. Also, can SYSENTER trap from guest userspace ring 3 into guest
kernelspace ring 1 on lhype?

Ingo