KVM: s390: add stat counter for shadow gmap events

The shadow gmap tracks memory of nested guests (guest-3). In certain
scenarios, the shadow gmap needs to be rebuilt, which is a costly operation
since it involves a SIE exit into guest-1 for every entry in the respective
shadow level.

Add kvm stat counters when new shadow structures are created at various
levels. Also add a counter gmap_shadow_create when a completely fresh
shadow gmap is created as well as a counter gmap_shadow_reuse when an
existing gmap is being reused.

Note that when several levels are shadowed at once, counters on all
affected levels will be increased.

Also note that not all page table levels need to be present and a ASCE
can directly point to e.g. a segment table. In this case, a new segment
table will always be equivalent to a new shadow gmap and hence will be
counted as gmap_shadow_create and not as gmap_shadow_segment.

Signed-off-by: Nico Boehr <[e-mail]>
Reviewed-by: David Hildenbrand <[e-mail]>
Reviewed-by: Claudio Imbrenda <[e-mail]>
Reviewed-by: Janosch Frank <[e-mail]>
Signed-off-by: Janosch Frank <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Message-Id: <[e-mail]>

arch/s390/include/asm/kvm_host.h

···
 	u64 inject_service_signal;
 	u64 inject_virtio;
 	u64 aen_forward;
+	u64 gmap_shadow_create;
+	u64 gmap_shadow_reuse;
+	u64 gmap_shadow_r1_entry;
+	u64 gmap_shadow_r2_entry;
+	u64 gmap_shadow_r3_entry;
+	u64 gmap_shadow_sg_entry;
+	u64 gmap_shadow_pg_entry;
 };
 
 struct kvm_arch_memory_slot {

arch/s390/kvm/gaccess.c

···
 				  unsigned long *pgt, int *dat_protection,
 				  int *fake)
 {
+	struct kvm *kvm;
 	struct gmap *parent;
 	union asce asce;
 	union vaddress vaddr;
···
 
 	*fake = 0;
 	*dat_protection = 0;
+	kvm = sg->private;
 	parent = sg->parent;
 	vaddr.addr = saddr;
 	asce.val = sg->orig_asce;
···
 		rc = gmap_shadow_r2t(sg, saddr, rfte.val, *fake);
 		if (rc)
 			return rc;
+		kvm->stat.gmap_shadow_r1_entry++;
 	}
 		fallthrough;
 	case ASCE_TYPE_REGION2: {
···
 		rc = gmap_shadow_r3t(sg, saddr, rste.val, *fake);
 		if (rc)
 			return rc;
+		kvm->stat.gmap_shadow_r2_entry++;
 	}
 		fallthrough;
 	case ASCE_TYPE_REGION3: {
···
 		rc = gmap_shadow_sgt(sg, saddr, rtte.val, *fake);
 		if (rc)
 			return rc;
+		kvm->stat.gmap_shadow_r3_entry++;
 	}
 		fallthrough;
 	case ASCE_TYPE_SEGMENT: {
···
 		rc = gmap_shadow_pgt(sg, saddr, ste.val, *fake);
 		if (rc)
 			return rc;
+		kvm->stat.gmap_shadow_sg_entry++;
 	}
 	}
 	/* Return the parent address of the page table */
···
 	pte.p |= dat_protection;
 	if (!rc)
 		rc = gmap_shadow_page(sg, saddr, __pte(pte.val));
+	vcpu->kvm->stat.gmap_shadow_pg_entry++;
 	ipte_unlock(vcpu->kvm);
 	mmap_read_unlock(sg->mm);
 	return rc;

arch/s390/kvm/kvm-s390.c

···
 	STATS_DESC_COUNTER(VM, inject_pfault_done),
 	STATS_DESC_COUNTER(VM, inject_service_signal),
 	STATS_DESC_COUNTER(VM, inject_virtio),
-	STATS_DESC_COUNTER(VM, aen_forward)
+	STATS_DESC_COUNTER(VM, aen_forward),
+	STATS_DESC_COUNTER(VM, gmap_shadow_reuse),
+	STATS_DESC_COUNTER(VM, gmap_shadow_create),
+	STATS_DESC_COUNTER(VM, gmap_shadow_r1_entry),
+	STATS_DESC_COUNTER(VM, gmap_shadow_r2_entry),
+	STATS_DESC_COUNTER(VM, gmap_shadow_r3_entry),
+	STATS_DESC_COUNTER(VM, gmap_shadow_sg_entry),
+	STATS_DESC_COUNTER(VM, gmap_shadow_pg_entry),
 };
 
 const struct kvm_stats_header kvm_vm_stats_header = {

arch/s390/kvm/vsie.c

···
 	 * we're holding has been unshadowed. If the gmap is still valid,
 	 * we can safely reuse it.
 	 */
-	if (vsie_page->gmap && gmap_shadow_valid(vsie_page->gmap, asce, edat))
+	if (vsie_page->gmap && gmap_shadow_valid(vsie_page->gmap, asce, edat)) {
+		vcpu->kvm->stat.gmap_shadow_reuse++;
 		return 0;
+	}
 
 	/* release the old shadow - if any, and mark the prefix as unmapped */
 	release_gmap_shadow(vsie_page);
···
 	if (IS_ERR(gmap))
 		return PTR_ERR(gmap);
 	gmap->private = vcpu->kvm;
+	vcpu->kvm->stat.gmap_shadow_create++;
 	WRITE_ONCE(vsie_page->gmap, gmap);
 	return 0;
 }