Re: [PATCH v6 4/5] KVM: s390x: Dirty quota-based throttling of vcpus

[Christian Borntraeger <borntraeger@linux.ibm.com>]

Am 15.09.22 um 12:10 schrieb Shivam Kumar:
> Exit to userspace whenever the dirty quota is exhausted (i.e. dirty count
> equals/exceeds dirty quota) to request more dirty quota.
> 
> Suggested-by: Shaju Abraham <shaju.abraham@nutanix.com>
> Suggested-by: Manish Mishra <manish.mishra@nutanix.com>
> Co-developed-by: Anurag Madnawat <anurag.madnawat@nutanix.com>
> Signed-off-by: Anurag Madnawat <anurag.madnawat@nutanix.com>
> Signed-off-by: Shivam Kumar <shivam.kumar1@nutanix.com>
> ---
>   arch/s390/kvm/kvm-s390.c | 9 +++++++++
>   1 file changed, 9 insertions(+)
> 
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index edfd4bbd0cba..2fe2933a7064 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -4343,6 +4343,15 @@ static int kvm_s390_handle_requests(struct kvm_vcpu *vcpu)
>   		goto retry;
>   	}
>   
> +	if (kvm_check_request(KVM_REQ_DIRTY_QUOTA_EXIT, vcpu)) {
> +		struct kvm_run *run = vcpu->run;
> +
> +		run->exit_reason = KVM_EXIT_DIRTY_QUOTA_EXHAUSTED;
> +		run->dirty_quota_exit.count = vcpu->stat.generic.pages_dirtied;
> +		run->dirty_quota_exit.quota = vcpu->dirty_quota;
> +		return 1;
> +	}

Please use
return -EREMOTE;

We use this in s390 code to indicate "we need exit to userspace" and
kvm_arch_vcpu_ioctl_run will change -EREMOTE to 0.

> +
>   	/* nothing to do, just clear the request */
>   	kvm_clear_request(KVM_REQ_UNHALT, vcpu);
>   	/* we left the vsie handler, nothing to do, just clear the request */