KVM: s390: implement CPU model only facilities

Some facilities should only be provided to the guest, if they are
enabled by a CPU model. This allows us to avoid capabilities and
to simply fall back to the cpumodel for deciding about a facility
without enabling it for older QEMUs or QEMUs without a CPU
model.
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

arch/s390/kvm/kvm-s390.c

@@ -152,13 +152,33 @@ static int nested;
 module_param(nested, int, S_IRUGO);
 MODULE_PARM_DESC(nested, "Nested virtualization support");
 
-/* upper facilities limit for kvm */
-unsigned long kvm_s390_fac_list_mask[16] = { FACILITIES_KVM };
 
-unsigned long kvm_s390_fac_list_mask_size(void)
+/*
+ * For now we handle at most 16 double words as this is what the s390 base
+ * kernel handles and stores in the prefix page. If we ever need to go beyond
+ * this, this requires changes to code, but the external uapi can stay.
+ */
+#define SIZE_INTERNAL 16
+
+/*
+ * Base feature mask that defines default mask for facilities. Consists of the
+ * defines in FACILITIES_KVM and the non-hypervisor managed bits.
+ */
+static unsigned long kvm_s390_fac_base[SIZE_INTERNAL] = { FACILITIES_KVM };
+/*
+ * Extended feature mask. Consists of the defines in FACILITIES_KVM_CPUMODEL
+ * and defines the facilities that can be enabled via a cpu model.
+ */
+static unsigned long kvm_s390_fac_ext[SIZE_INTERNAL] = { FACILITIES_KVM_CPUMODEL };
+
+static unsigned long kvm_s390_fac_size(void)
 {
-	BUILD_BUG_ON(ARRAY_SIZE(kvm_s390_fac_list_mask) > S390_ARCH_FAC_MASK_SIZE_U64);
-	return ARRAY_SIZE(kvm_s390_fac_list_mask);
+	BUILD_BUG_ON(SIZE_INTERNAL > S390_ARCH_FAC_MASK_SIZE_U64);
+	BUILD_BUG_ON(SIZE_INTERNAL > S390_ARCH_FAC_LIST_SIZE_U64);
+	BUILD_BUG_ON(SIZE_INTERNAL * sizeof(unsigned long) >
+		sizeof(S390_lowcore.stfle_fac_list));
+
+	return SIZE_INTERNAL;
 }
 
 /* available cpu features supported by kvm */
@@ -1967,20 +1987,15 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
 	if (!kvm->arch.sie_page2)
 		goto out_err;
 
-	/* Populate the facility mask initially. */
-	memcpy(kvm->arch.model.fac_mask, S390_lowcore.stfle_fac_list,
-	       sizeof(S390_lowcore.stfle_fac_list));
-	for (i = 0; i < S390_ARCH_FAC_LIST_SIZE_U64; i++) {
-		if (i < kvm_s390_fac_list_mask_size())
-			kvm->arch.model.fac_mask[i] &= kvm_s390_fac_list_mask[i];
-		else
-			kvm->arch.model.fac_mask[i] = 0UL;
-	}
-
-	/* Populate the facility list initially. */
 	kvm->arch.model.fac_list = kvm->arch.sie_page2->fac_list;
-	memcpy(kvm->arch.model.fac_list, kvm->arch.model.fac_mask,
-	       S390_ARCH_FAC_LIST_SIZE_BYTE);
+
+	for (i = 0; i < kvm_s390_fac_size(); i++) {
+		kvm->arch.model.fac_mask[i] = S390_lowcore.stfle_fac_list[i] &
+					      (kvm_s390_fac_base[i] |
+					       kvm_s390_fac_ext[i]);
+		kvm->arch.model.fac_list[i] = S390_lowcore.stfle_fac_list[i] &
+					      kvm_s390_fac_base[i];
+	}
 
 	/* we are always in czam mode - even on pre z14 machines */
 	set_kvm_facility(kvm->arch.model.fac_mask, 138);
@@ -4044,7 +4059,7 @@ static int __init kvm_s390_init(void)
 	}
 
 	for (i = 0; i < 16; i++)
-		kvm_s390_fac_list_mask[i] |=
+		kvm_s390_fac_base[i] |=
 			S390_lowcore.stfle_fac_list[i] & nonhyp_mask(i);
 
 	return kvm_init(NULL, sizeof(struct kvm_vcpu), 0, THIS_MODULE);

arch/s390/kvm/kvm-s390.h

@@ -294,8 +294,6 @@ void exit_sie(struct kvm_vcpu *vcpu);
 void kvm_s390_sync_request(int req, struct kvm_vcpu *vcpu);
 int kvm_s390_vcpu_setup_cmma(struct kvm_vcpu *vcpu);
 void kvm_s390_vcpu_unsetup_cmma(struct kvm_vcpu *vcpu);
-unsigned long kvm_s390_fac_list_mask_size(void);
-extern unsigned long kvm_s390_fac_list_mask[];
 void kvm_s390_set_cpu_timer(struct kvm_vcpu *vcpu, __u64 cputm);
 __u64 kvm_s390_get_cpu_timer(struct kvm_vcpu *vcpu);
 

arch/s390/tools/gen_facilities.c

@@ -62,6 +62,13 @@ static struct facility_def facility_defs[] = {
 		}
 	},
 	{
+		/*
+		 * FACILITIES_KVM contains the list of facilities that are part
+		 * of the default facility mask and list that are passed to the
+		 * initial CPU model. If no CPU model is used, this, together
+		 * with the non-hypervisor managed bits, is the maximum list of
+		 * guest facilities supported by KVM.
+		 */
 		.name = "FACILITIES_KVM",
 		.bits = (int[]){
 			0,  /* N3 instructions */
@@ -89,6 +96,19 @@ static struct facility_def facility_defs[] = {
 			-1  /* END */
 		}
 	},
+	{
+		/*
+		 * FACILITIES_KVM_CPUMODEL contains the list of facilities
+		 * that can be enabled by CPU model code if the host supports
+		 * it. These facilities are not passed to the guest without
+		 * CPU model support.
+		 */
+
+		.name = "FACILITIES_KVM_CPUMODEL",
+		.bits = (int[]){
+			-1  /* END */
+		}
+	},
 };
 
 static void print_facility_list(struct facility_def *def)