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Subject: Re: [PATCH v1 10/11] KVM: s390: pv: module parameter to fence lazy
 destroy
To:     Claudio Imbrenda <imbrenda@linux.ibm.com>, kvm@vger.kernel.org
Cc:     cohuck@redhat.com, borntraeger@de.ibm.com, thuth@redhat.com,
        pasic@linux.ibm.com, david@redhat.com, linux-s390@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20210517200758.22593-1-imbrenda@linux.ibm.com>
 <20210517200758.22593-11-imbrenda@linux.ibm.com>
From:   Janosch Frank <frankja@linux.ibm.com>
Message-ID: <7b43f05f-30e0-1c84-74f1-c28fdd6fcff4@linux.ibm.com>
Date:   Thu, 27 May 2021 12:35:38 +0200
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On 5/17/21 10:07 PM, Claudio Imbrenda wrote:
> Add the module parameter "lazy_destroy", to allow the lazy destroy
> mechanism to be switched off. This might be useful for debugging
> purposes.
> 
> The parameter is enabled by default.
> 
> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
> ---
>  arch/s390/kvm/pv.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/arch/s390/kvm/pv.c b/arch/s390/kvm/pv.c
> index 4333d3e54ef0..00c14406205f 100644
> --- a/arch/s390/kvm/pv.c
> +++ b/arch/s390/kvm/pv.c
> @@ -26,6 +26,10 @@ struct deferred_priv {
>  	unsigned long real;
>  };
>  
> +static int lazy_destroy = 1;
> +module_param(lazy_destroy, int, 0444);

I'm pondering if we want to make that writable or not.

Reviewed-by: Janosch Frank <frankja@linux.ibm.com>

> +MODULE_PARM_DESC(lazy_destroy, "Deferred destroy for protected guests");
> +
>  int kvm_s390_pv_destroy_cpu(struct kvm_vcpu *vcpu, u16 *rc, u16 *rrc)
>  {
>  	int cc = 0;
> @@ -348,6 +352,9 @@ int kvm_s390_pv_deinit_vm_deferred(struct kvm *kvm, u16 *rc, u16 *rrc)
>  {
>  	struct deferred_priv *priv;
>  
> +	if (!lazy_destroy)
> +		kvm_s390_pv_deinit_vm_now(kvm, rc, rrc);
> +
>  	priv = kmalloc(sizeof(*priv), GFP_KERNEL | __GFP_ZERO);
>  	if (!priv)
>  		return kvm_s390_pv_deinit_vm_now(kvm, rc, rrc);
> @@ -396,6 +403,12 @@ int kvm_s390_pv_init_vm(struct kvm *kvm, u16 *rc, u16 *rrc)
>  	/* Outputs */
>  	kvm->arch.pv.handle = uvcb.guest_handle;
>  
> +	if (!lazy_destroy) {
> +		mmap_write_lock(kvm->mm);
> +		kvm->mm->context.pv_sync_destroy = 1;
> +		mmap_write_unlock(kvm->mm);
> +	}
> +
>  	atomic_inc(&kvm->mm->context.is_protected);
>  	if (cc) {
>  		if (uvcb.header.rc & UVC_RC_NEED_DESTROY) {
>