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 <nrb@linux.ibm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
Link: https://lore.kernel.org/r/20231009093304.2555344-2-nrb@linux.ibm.com
Message-Id: <20231009093304.2555344-2-nrb@linux.ibm.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/arch/s390/kvm/gaccess.c b/arch/s390/kvm/gaccess.c
index 6d6bc19b37dc..ff8349d17b33 100644
--- a/arch/s390/kvm/gaccess.c
+++ b/arch/s390/kvm/gaccess.c
@@ -1382,6 +1382,7 @@ static int kvm_s390_shadow_tables(struct gmap *sg, unsigned long saddr,
 				  unsigned long *pgt, int *dat_protection,
 				  int *fake)
 {
+	struct kvm *kvm;
 	struct gmap *parent;
 	union asce asce;
 	union vaddress vaddr;
@@ -1390,6 +1391,7 @@ static int kvm_s390_shadow_tables(struct gmap *sg, unsigned long saddr,
 
 	*fake = 0;
 	*dat_protection = 0;
+	kvm = sg->private;
 	parent = sg->parent;
 	vaddr.addr = saddr;
 	asce.val = sg->orig_asce;
@@ -1450,6 +1452,7 @@ shadow_r2t:
 		rc = gmap_shadow_r2t(sg, saddr, rfte.val, *fake);
 		if (rc)
 			return rc;
+		kvm->stat.gmap_shadow_r1_entry++;
 	}
 		fallthrough;
 	case ASCE_TYPE_REGION2: {
@@ -1478,6 +1481,7 @@ shadow_r3t:
 		rc = gmap_shadow_r3t(sg, saddr, rste.val, *fake);
 		if (rc)
 			return rc;
+		kvm->stat.gmap_shadow_r2_entry++;
 	}
 		fallthrough;
 	case ASCE_TYPE_REGION3: {
@@ -1515,6 +1519,7 @@ shadow_sgt:
 		rc = gmap_shadow_sgt(sg, saddr, rtte.val, *fake);
 		if (rc)
 			return rc;
+		kvm->stat.gmap_shadow_r3_entry++;
 	}
 		fallthrough;
 	case ASCE_TYPE_SEGMENT: {
@@ -1548,6 +1553,7 @@ shadow_pgt:
 		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 */
@@ -1618,6 +1624,7 @@ shadow_page:
 	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;