[PATCH v2 16/20] KVM: s390: vsie: Allow guest-3 cpu add and remove with ssca

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 <[email protected]>
---
 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 844ffd3244fe..3ae346265b81 100644
--- a/arch/s390/kvm/vsie.c
+++ b/arch/s390/kvm/vsie.c
@@ -2051,6 +2051,43 @@ 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)
 {
@@ -2070,18 +2107,16 @@ 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;
@@ -2117,23 +2152,36 @@ 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