Re: [PATCH RFC v2 11/11] KVM: s390: Add VSIE shadow stat counters

[Janosch Frank <frankja@linux.ibm.com>]

On 11/10/25 18:16, Christoph Schlameuss wrote:
> Add new stat counters to VSIE shadowing to be able to verify and monitor
> the functionality.
> 
> * vsie_shadow_scb shows the number of allocated SIE control block
>    shadows. Should count upwards between 0 and the max number of cpus.
> * vsie_shadow_sca shows the number of allocated system control area
>    shadows. Should count upwards between 0 and the max number of cpus.
> * vsie_shadow_sca_create shows the number of newly allocated system
>    control area shadows.
> * vsie_shadow_sca_reuse shows the number of reused system control area
>    shadows.
> 
> Signed-off-by: Christoph Schlameuss <schlameuss@linux.ibm.com>
> ---
>   arch/s390/include/asm/kvm_host.h | 4 ++++
>   arch/s390/kvm/kvm-s390.c         | 4 ++++
>   arch/s390/kvm/vsie.c             | 9 ++++++++-
>   3 files changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
> index 191b23edf0ac7e9a3e1fd9cdc6fc4c9a9e6769f8..ef7bf2d357f8d289b5f163ec95976c5d270d1380 100644
> --- a/arch/s390/include/asm/kvm_host.h
> +++ b/arch/s390/include/asm/kvm_host.h
> @@ -457,6 +457,10 @@ struct kvm_vm_stat {
>   	u64 gmap_shadow_r3_entry;
>   	u64 gmap_shadow_sg_entry;
>   	u64 gmap_shadow_pg_entry;
> +	u64 vsie_shadow_scb;
> +	u64 vsie_shadow_sca;
> +	u64 vsie_shadow_sca_create;
> +	u64 vsie_shadow_sca_reuse;
>   };
>   
>   struct kvm_arch_memory_slot {
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index e3fc53e33e90be7dab75f73ebd0b949c13d22939..d86bf2206c230ce25fd48610c8305326e260e590 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -79,6 +79,10 @@ const struct _kvm_stats_desc kvm_vm_stats_desc[] = {
>   	STATS_DESC_COUNTER(VM, gmap_shadow_r3_entry),
>   	STATS_DESC_COUNTER(VM, gmap_shadow_sg_entry),
>   	STATS_DESC_COUNTER(VM, gmap_shadow_pg_entry),
> +	STATS_DESC_COUNTER(VM, vsie_shadow_scb),
> +	STATS_DESC_COUNTER(VM, vsie_shadow_sca),
> +	STATS_DESC_COUNTER(VM, vsie_shadow_sca_create),
> +	STATS_DESC_COUNTER(VM, vsie_shadow_sca_reuse),
>   };
>   
>   const struct kvm_stats_header kvm_vm_stats_header = {
> diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c
> index cd114df5e119bd289d14037d1f1c5bfe148cf5c7..f7c1a217173cefe93d0914623df08efa14270771 100644
> --- a/arch/s390/kvm/vsie.c
> +++ b/arch/s390/kvm/vsie.c
> @@ -767,6 +767,8 @@ static int shadow_scb(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
>   out:
>   	if (rc)
>   		unshadow_scb(vcpu, vsie_page);
> +	else
> +		vcpu->kvm->stat.vsie_shadow_scb++;
>   	return rc;
>   }
>   
> @@ -843,8 +845,10 @@ static struct vsie_sca *get_existing_vsie_sca(struct kvm *kvm, hpa_t sca_o_gpa)
>   {
>   	struct vsie_sca *sca = radix_tree_lookup(&kvm->arch.vsie.osca_to_sca, sca_o_gpa);
>   
> -	if (sca)
> +	if (sca) {
>   		WARN_ON_ONCE(atomic_inc_return(&sca->ref_count) < 1);
> +		kvm->stat.vsie_shadow_sca_reuse++;
> +	}
>   	return sca;
>   }
>   
> @@ -958,6 +962,8 @@ static struct vsie_sca *get_vsie_sca(struct kvm_vcpu *vcpu, struct vsie_page *vs
>   		sca_new = NULL;
>   
>   		kvm->arch.vsie.scas[kvm->arch.vsie.sca_count] = sca;
> +		kvm->arch.vsie.sca_count++;

Why are you touching a non-stat variable in this patch?


> +		kvm->stat.vsie_shadow_sca++;
>   	} else {
>   		/* reuse previously created vsie_sca allocation for different osca */
>   		sca = get_free_existing_vsie_sca(kvm);
> @@ -992,6 +998,7 @@ static struct vsie_sca *get_vsie_sca(struct kvm_vcpu *vcpu, struct vsie_page *vs
>   
>   	atomic_set(&sca->ref_count, 1);
>   	radix_tree_insert(&kvm->arch.vsie.osca_to_sca, sca->sca_gpa, sca);
> +	kvm->stat.vsie_shadow_sca_create++;
>   
>   out:
>   	up_write(&kvm->arch.vsie.ssca_lock);
>