[PATCH] KVM: s390: implement CPU model only facilities

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Some facilities should only provided to the guest, if these are
enabled by a CPU model. This allows to avoid capabilities and
simply fallback to the cpumodel for deciding about a facility
without enabling it for older QEMUs or QEMUs without a CPU
model.

Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
---
 arch/s390/kvm/kvm-s390.c         | 40 ++++++++++++++++++++++++++++++++--------
 arch/s390/kvm/kvm-s390.h         |  2 --
 arch/s390/tools/gen_facilities.c | 20 ++++++++++++++++++++
 3 files changed, 52 insertions(+), 10 deletions(-)

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 5b7fe80cda56..7d982690b1fc 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -151,13 +151,27 @@ 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 not more than 16 double words as this is what
+ * the s390 base kernel handles and stores in 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
+
+/* upper facilities limit for kvm */
+static unsigned long kvm_s390_fac_list_mask[SIZE_INTERNAL] = { FACILITIES_KVM };
+/*
+ * facility bits that are in the mask, but initially not in the list.
+ * Those can be activated by the CPU model
+ */
+static unsigned long kvm_s390_fac_model[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);
+	return SIZE_INTERNAL;
 }
 
 /* available cpu features supported by kvm */
@@ -1946,17 +1960,27 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
 	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];
+		if (i < kvm_s390_fac_size())
+			kvm->arch.model.fac_mask[i] &= (kvm_s390_fac_list_mask[i] |
+							kvm_s390_fac_model[i]);
 		else
 			kvm->arch.model.fac_mask[i] = 0UL;
 	}
 
-	/* Populate the facility list initially. */
+	/* Populate the facility list initially as a copy of the mask */
 	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);
 
+	/*
+	 * Disable facilities in the list that need CPU model support.
+	 * Those are now in the mask but not in the list. Userspace can
+	 * re-enable those that are in the mask via the CPU model
+	 */
+	for (i = 0; i < S390_ARCH_FAC_LIST_SIZE_U64; i++)
+		if (i < kvm_s390_fac_size())
+			kvm->arch.model.fac_list[i] &= ~kvm_s390_fac_model[i];
+
 	/* we are always in czam mode - even on pre z14 machines */
 	set_kvm_facility(kvm->arch.model.fac_mask, 138);
 	set_kvm_facility(kvm->arch.model.fac_list, 138);
diff --git a/arch/s390/kvm/kvm-s390.h b/arch/s390/kvm/kvm-s390.h
index 3c0a975c2477..75efb6835acc 100644
--- a/arch/s390/kvm/kvm-s390.h
+++ b/arch/s390/kvm/kvm-s390.h
@@ -295,8 +295,6 @@ 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);
 
diff --git a/arch/s390/tools/gen_facilities.c b/arch/s390/tools/gen_facilities.c
index 424a1ba4f874..37a77a3f280c 100644
--- a/arch/s390/tools/gen_facilities.c
+++ b/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 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)
-- 
2.14.3

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