On 15.07.2013, at 22:52, Scott Wood wrote:
> 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?
No, because it would be the guest that doesn't know how to handle kvm
hypercalls.
> 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.
That's my point :).
Alex
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