Re: [PATCH v4] KVM: s390: Add new reset vcpu API

[Thomas Huth <thuth@redhat.com>]

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On 09/01/2020 18.51, Janosch Frank wrote:
> On 1/9/20 6:08 PM, Cornelia Huck wrote:
>> On Thu,  9 Jan 2020 10:56:01 -0500
>> Janosch Frank <frankja@linux.ibm.com> wrote:
>>
>>> The architecture states that we need to reset local IRQs for all CPU
>>> resets. Because the old reset interface did not support the normal CPU
>>> reset we never did that on a normal reset.
>>>
>>> Let's implement an interface for the missing normal and clear resets
>>> and reset all local IRQs, registers and control structures as stated
>>> in the architecture.
>>>
>>> Userspace might already reset the registers via the vcpu run struct,
>>> but as we need the interface for the interrupt clearing part anyway,
>>> we implement the resets fully and don't rely on userspace to reset the
>>> rest.
>>>
>>> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
>>> ---
>>>
>>> I dropped the reviews, as I changed quite a lot.  
>>>
>>> Keep in mind, that now we'll need a new parameter in normal and
>>> initial reset for protected virtualization to indicate that we need to
>>> do the reset via the UV call. The Ultravisor does only accept the
>>> needed reset, not any subset resets.
>>
>> In the interface, or externally?
> 
> ?
> 
>>
>> [Apologies, but the details of the protected virt stuff are no longer
>> in my cache.
> Reworded explanation:
> I can't use a fallthrough, because the UV will reject the normal reset
> if we do an initial reset (same goes for the clear reset). To address
> this issue, I added a boolean to the normal and initial reset functions
> which tells the function if it was called directly or was called because
> of the fallthrough.
> 
> Only if called directly a UV call for the reset is done, that way we can
> keep the fallthrough.

Sounds complicated. And do we need the fallthrough stuff here at all?
What about doing something like:

static int kvm_arch_vcpu_ioctl_normal_reset(struct kvm_vcpu *vcpu)
{
	...
}

static int kvm_arch_vcpu_ioctl_initial_reset(struct kvm_vcpu *vcpu)
{
	kvm_arch_vcpu_ioctl_normal_reset(vcpu);
	...
}

static int kvm_arch_vcpu_ioctl_clear_reset(struct kvm_vcpu *vcpu)
{
	kvm_arch_vcpu_ioctl_initial_reset(vcpu);
	...
}

...

	case KVM_S390_CLEAR_RESET:
		r = kvm_arch_vcpu_ioctl_clear_reset(vcpu);
		if (!r && protected) {
			r = uv_cmd_nodata(...,
 				UVC_CMD_CPU_RESET_CLEAR, ...);
		}
		break;
 	case KVM_S390_INITIAL_RESET:
 		r = kvm_arch_vcpu_ioctl_initial_reset(vcpu);
		if (!r && protected) {
			r = uv_cmd_nodata(...,
 				UVC_CMD_CPU_RESET_INITIAL, ...);
		}
	case KVM_S390_NORMAL_RESET:
		r = kvm_arch_vcpu_ioctl_normal_reset(vcpu);
		if (!r && protected) {
			r = uv_cmd_nodata(...,
 				UVC_CMD_CPU_RESET, ...);
		}
 		break;

... or does that not work due to some other constraints that I've missed?

 Thomas


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