As we are shadowing the SCA we need to add and remove the pointers to
the shadowed control blocks and sca entries whenever the mcn /
processors in the configuration changes.

It is not expected that the mcn changes frequently for an already
running guest-3 configuration. So we can simply fully re-init the ssca
whenever the mcn changes.
To detect the mcn change we store the expected mcn in the struct
vsie_sca when running _shadow_sca().

Signed-off-by: Christoph Schlameuss <schlameuss@linux.ibm.com>
---
 arch/s390/kvm/vsie.c | 68 ++++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 58 insertions(+), 10 deletions(-)

diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c
index 154772278d0a..6088a9c31564 100644
--- a/arch/s390/kvm/vsie.c
+++ b/arch/s390/kvm/vsie.c
@@ -2052,6 +2052,43 @@ static struct vsie_page *get_vsie_page_cpu_nr(struct kvm_vcpu *vcpu, struct vsie
 	return vsie_page;
 }
 
+/*
+ * Copy the mcn from the osca to the vsie_sca to be able to detect mcn changes later on.
+ *
+ * @vsie_sca: vsie_sca to copy mcn to.
+ * @sca: Pointer to a struct bsca_block or struct esca_block to read from.
+ */
+static void sca_mcn_copy(struct vsie_sca *vsie_sca, void *sca)
+{
+	int offset = offsetof(struct bsca_block, mcn);
+	int size = sizeof(unsigned long);
+
+	if (test_bit(VSIE_SCA_ESCA, &vsie_sca->flags)) {
+		offset = offsetof(struct esca_block, mcn);
+		size = size * 4;
+	}
+	memcpy(&vsie_sca->mcn, sca + offset, size);
+}
+
+/*
+ * Compare the mcn from the given sca to the vsie_sca to be able to detect mcn changes.
+ *
+ * @vsie_sca: vsie_sca to compare mcn to.
+ * @sca: Pointer to a struct bsca_block or struct esca_block to compare to.
+ */
+static bool sca_mcn_equals(struct vsie_sca *vsie_sca, void *sca)
+{
+	int offset = offsetof(struct bsca_block, mcn);
+	int size = sizeof(unsigned long);
+
+	if (test_bit(VSIE_SCA_ESCA, &vsie_sca->flags)) {
+		size = size * 4;
+		offset = offsetof(struct esca_block, mcn);
+	}
+
+	return !memcmp(&vsie_sca->mcn, sca + offset, size);
+}
+
 static void vsie_sca_update(struct vsie_sca *vsie_sca, unsigned int cpu_nr,
 			    struct vsie_page *vsie_page_n, hpa_t sca_o_entry_hpa)
 {
@@ -2071,18 +2108,16 @@ static int _shadow_sca(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page,
 	struct vsie_page *vsie_page_n;
 	hpa_t sca_o_entry_hpa;
 	hva_t sca_o_entry_hva;
-	unsigned long *mcn;
 	gpa_t scb_o_gpa;
 	int rc;
 
 	if (is_esca)
-		mcn = phys_to_virt(sca_o_hpa(vsie_sca)) + offsetof(struct esca_block, mcn);
-	else
-		mcn = phys_to_virt(sca_o_hpa(vsie_sca)) + offsetof(struct bsca_block, mcn);
+		__set_bit(VSIE_SCA_ESCA, &vsie_sca->flags);
+	sca_mcn_copy(vsie_sca, phys_to_virt(sca_o_hpa(vsie_sca)));
 
 	/* pin and make shadow for ALL scb in the sca */
 	cpu_slots = is_esca ? KVM_S390_MAX_VSIE_VCPUS : KVM_S390_BSCA_CPU_SLOTS;
-	for_each_set_bit_inv(cpu_nr, mcn, cpu_slots) {
+	for_each_set_bit_inv(cpu_nr, (unsigned long *)&vsie_sca->mcn, cpu_slots) {
 		rc = get_sca_entry_addr(vcpu->kvm, vsie_sca, cpu_nr, NULL, &sca_o_entry_hpa);
 		if (rc)
 			goto err;
@@ -2118,23 +2153,36 @@ static int _shadow_sca(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page,
 	return 0;
 
 err:
-	for_each_set_bit_inv(cpu_nr, mcn, cpu_slots) {
+	vsie_sca->ssca.osca = 0;
+	for_each_set_bit_inv(cpu_nr, (unsigned long *)&vsie_sca->mcn, cpu_slots) {
 		vsie_sca->ssca.cpu[cpu_nr].ssda = 0;
 		vsie_sca->ssca.cpu[cpu_nr].ossea = 0;
 	}
 	return rc;
 }
 
+static bool config_changed(struct vsie_page *vsie_page, struct vsie_sca *vsie_sca)
+{
+	bool changed = !vsie_sca->ssca.osca;
+
+	changed = changed || sie_uses_esca(vsie_page->scb_o) !=
+			     test_bit(VSIE_SCA_ESCA, &vsie_sca->flags);
+	return changed || !sca_mcn_equals(vsie_sca, phys_to_virt(sca_o_hpa(vsie_sca)));
+}
+
 /* Shadow or reshadow the SCA on VSIE enter. */
 static int shadow_sca(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page, struct vsie_sca *vsie_sca)
 {
-	int rc = 0;
+	scoped_guard(rwsem_read, &vcpu->kvm->arch.vsie.vsie_sca_lock) {
+		if (!config_changed(vsie_page, vsie_sca))
+			return 0;
+	}
 
 	guard(rwsem_write)(&vcpu->kvm->arch.vsie.vsie_sca_lock);
-	if (!vsie_sca->ssca.osca)
-		rc = _shadow_sca(vcpu, vsie_page, vsie_sca);
+	if (!config_changed(vsie_page, vsie_sca))
+		return 0;
 
-	return rc;
+	return _shadow_sca(vcpu, vsie_page, vsie_sca);
 }
 
 int kvm_s390_handle_vsie(struct kvm_vcpu *vcpu)

-- 
2.55.0