[Qemu-devel] Re: [PATCH 4/5] kvmppc: Translate eaddr for fsl_booke mmu

[Alexander Graf]

On 24.08.2009, at 19:33, Hollis Blanchard wrote:

> On Mon, 2009-08-24 at 10:44 +0800, Liu Yu-B13201 wrote:
> > > IMHO userspace should do the translation and do an ioctl to
> > > fetch the
> > > required information (soft TLB cache / SLB / SDR1) so we can
> > > reuse the
> > > existing qemu infrastructure.
> >
> > BOOK3S has mmu implement in qemu, but BOOKE doesn't.
>
> Even if it did, I'd be skeptical. But you're right that that's a
> critical point: as things stand today, only KVM (not qemu) emulates  
> the
> Book E MMU.

Well, that's the whole point I was trying to make.

If we had the booke mmu implemented in qemu debugging would be a lot  
easier I guess. Also it'd benefit people who for whatever reason want  
to emulate a booke cpu instead of virtualizing one, maybe because  
their development machines are x86 ;-).

If I remember the x86 KVM architecture correctly, CR3 (the register  
holding a phys addr to the current pagetable) gets pulled by userspace  
and then qemu does the complete translation based on that information.

So yes, we do have two separate MMU implementations for x86 here, but  
that's a good thing IMHO, because it makes it easier to spot bugs and  
find out where things went wrong.

So my suggestion is: Implement the BOOKE MMU in Qemu, make an IOCTL to  
pull the TLB to userspace and thus make life easier for everyone.

Alex