Re: [PATCH v1 10/11] KVM: s390: pv: module parameter to fence lazy destroy

Janosch Frank
2021-05-27T10:35:47Z

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) {
>