Re: [PATCH 09/10] KVM: PPC: Support SC1 hypercalls for PAPR in PR

David Gibson
2011-08-12T07:43:59Z

On Fri, Aug 12, 2011 at 07:35:42AM +0200, Alexander Graf wrote:
>
> Am 12.08.2011 um 05:33 schrieb David Gibson <david@gibson.dropbear.id.au>:
>
> > On Tue, Aug 09, 2011 at 06:31:47PM +0200, Alexander Graf wrote:
> >> PAPR defines hypercalls as SC1 instructions. Using these, the guest modifies
> >> page tables and does other privileged operations that it wouldn't be allowed
> >> to do in supervisor mode.
> >>
> >> This patch adds support for PR KVM to trap these instructions and route them
> >> through the same PAPR hypercall interface that we already use for HV style
> >> KVM.
> >
> > This will work on a powermac or bare metal host. Unfortunately, it's
> > not enough on a pSeries LPAR host - the sc 1 instruction from the
> > guest problem state will go direct to the hypervisor, which will
> > return an error rather than trapping to the guest kernel.
> >
> > The only way around this I can see is for qemu to search for and patch
> > up sc 1 instructions to something else. Obviously that would also
> > need some kernel support, and probably a capability to let it know if
> > it's necessary.
>
> Well I'd like to keep Qemu out of the patching business, so the
> guest kernel would have to patch itself.

Well sure, but guest patching itself means it can't run existing
kernels. I thought qemu already patched a few things, ugly though
that approach is.

> But yes, PHyP guests can't
> run this target yet :). I'll take a stab at that too, but one
> continent at a time! ;)

--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!