Re: [PATCH 5/5] powerpc: using reset hcall when kvm,has-reset

Scott Wood
2013-07-15T20:52:47Z

On 07/15/2013 03:28:46 PM, Alexander Graf wrote:
>
> On 15.07.2013, at 20:21, Scott Wood wrote:
>
> > On 07/15/2013 10:16:41 AM, Bhushan Bharat-R65777 wrote:
> >> > >>> + printk("error: system reset returned with error %ld\n",
> ret);
> >> > >>
> >> > >> So we should fall back to the normal reset handler here.
> >> > >
> >> > > Do you mean return normally from here, no BUG() etc?
> >> >
> >> > If we guard the patching against everything, we can treat a
> broken hcall as BUG.
> >> > However, if we don't we want to fall back to the normal guts
> based reset.
> >> Will let Scott comment on this?
> >> But ppc_md.restart can point to only one handler and during
> paravirt patching we changed this to new handler. So we cannot jump
> back to guts type handler
> >
> > I don't think it's worth implementing a fall-back scheme -- if KVM
> advertises that the reset hcall exists, then it had better exist.
>
> If we also check for kvm_para_available() I agree. Otherwise QEMU
> might advertise the reset hcall, but the guest kernel may not
> implement KVM hypercalls. In that case the device tree check will
> succeed, but the actual hypercall will not.

Wouldn't that be a bug in QEMU? Or in KVM for exposing the hcall
capability without implementing them?

Not that I have anything against checking kvm_para_available()...
though that (or its functional equivalent that returns a pointer to the
node) should really be a prerequisite for even being able to interpret
KVM-specific properties in the hypervisor node.

-Scott