[PATCH] KVM: PPC: Book3S HV: check for XIVE device before executing the XICS hcalls

[Cédric Le Goater]

On 12/04/2017 02:04 AM, Paul Mackerras wrote:
> On Mon, Nov 27, 2017 at 08:30:17AM +0100, Cédric Le Goater wrote:
>> When QEMU is started with the option kernel_irqchip=òff, the kvm XICS
>> hcalls are being used even though a kvm XICS device has not been
>> created on the host, resulting quickly in a failure and a broken
>> guest.
>>
>> The test checking if there is a XIVE device in the VM before executing
>> the XICS hcalls is missing from the recent XICS-over-XIVE glue.
>>
>> Signed-off-by: Cédric Le Goater <clg at kaod.org>
> 
> I think this is fixing the same bug that commit 00bb6ae50062 ("KVM:
> PPC: Book3S HV: Don't call real-mode XICS hypercall handlers if not
> enabled", 2017-10-26) addresses.
> 
> Do you think this patch is needed in addition to 00bb6ae50062?

No. I think 00bb6ae50062 is fine. 

It is a bit redundant for P8 systems because the XICS device 
availability in the VM is already tested in the xics_rm_h_* hcalls 
with : 
 
	struct kvmppc_xics *xics = vcpu->kvm->arch.xics;

	if (!xics || !xics->real_mode)
		return H_TOO_HARD;

But, as the XICS-over-XIVE glue also assigns the VCPU 'arch.irq_type' 
field to KVMPPC_IRQ_XICS, we can use the macro kvmppc_xics_enabled()
for both backend in the top level hcalls.

Letting each backend decide whether H_TOO_HARD should be returned 
might be more precise. I think we will clarify that when XIVE 
exploitation mode support is added to KVM.

Thanks,

C.