[PATCH v6 17/21] KVM: s390: vsie: Allow guest-3 cpu add and remove with ssca

[Christoph Schlameuss <schlameuss@linux.ibm.com>]

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/s390/vsie.c | 66 +++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 55 insertions(+), 11 deletions(-)

diff --git a/arch/s390/kvm/s390/vsie.c b/arch/s390/kvm/s390/vsie.c
index 16273cf5cbff..bfd5df1f8b9c 100644
--- a/arch/s390/kvm/s390/vsie.c
+++ b/arch/s390/kvm/s390/vsie.c
@@ -2093,6 +2093,43 @@ static int get_vsie_page_cpu_nr(struct kvm_vcpu *vcpu, struct vsie_sca *vsie_sca
 	return 0;
 }
 
+/*
+ * 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 update_vsie_sca(struct vsie_sca *vsie_sca, unsigned int cpu_nr,
 			    struct vsie_page *vsie_page_n, hpa_t sca_o_entry_hpa)
 {
@@ -2142,17 +2179,17 @@ static int _shadow_sca(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page,
 	bool is_esca = sie_uses_esca(vsie_page->scb_o);
 	unsigned int cpu_nr, cpu_slots;
 	hpa_t sca_o_entry_hpa;
-	unsigned long *mcn;
 	int rc;
 
 	if (is_esca)
-		mcn = phys_to_virt(sca_o_hpa(vsie_sca)) + offsetof(struct esca_block, mcn);
+		set_bit(VSIE_SCA_ESCA, &vsie_sca->flags);
 	else
-		mcn = phys_to_virt(sca_o_hpa(vsie_sca)) + offsetof(struct bsca_block, mcn);
+		clear_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)
 			break;
@@ -2179,19 +2216,26 @@ static int _shadow_sca(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page,
 	return rc;
 }
 
+static bool shadow_sca_needed(struct vsie_sca *vsie_sca)
+{
+	if (!vsie_sca->ssca.osca)
+		return true;
+	return !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 (!shadow_sca_needed(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 (!rc)
-		write_scao(&vsie_page->scb_s, virt_to_phys(&vsie_sca->ssca));
+	if (!shadow_sca_needed(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