KVM: s390: make cmma usage conditionally

When userspace reset the guest without notifying kvm, the CMMA state
of the pages might be unused, resulting in guest data corruption.
To avoid this, CMMA must be enabled only if userspace understands
the implications.

CMMA must be enabled before vCPU creation. It can't be switched off
once enabled.  All subsequently created vCPUs will be enabled for
CMMA according to the CMMA state of the VM.

Signed-off-by: Dominik Dingel <dingel@linux.vnet.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
[remove now unnecessary calls to page_table_reset_pgste]

arch/s390/kvm/kvm-s390.c

@@ -437,9 +437,8 @@ void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu)
 	if (kvm_is_ucontrol(vcpu->kvm))
 		gmap_free(vcpu->arch.gmap);
 
-	if (vcpu->arch.sie_block->cbrlo)
-		__free_page(__pfn_to_page(
-				vcpu->arch.sie_block->cbrlo >> PAGE_SHIFT));
+	if (kvm_s390_cmma_enabled(vcpu->kvm))
+		kvm_s390_vcpu_unsetup_cmma(vcpu);
 	free_page((unsigned long)(vcpu->arch.sie_block));
 
 	kvm_vcpu_uninit(vcpu);
@@ -553,9 +552,26 @@ int kvm_arch_vcpu_postcreate(struct kvm_vcpu *vcpu)
 	return 0;
 }
 
+void kvm_s390_vcpu_unsetup_cmma(struct kvm_vcpu *vcpu)
+{
+	free_page(vcpu->arch.sie_block->cbrlo);
+	vcpu->arch.sie_block->cbrlo = 0;
+}
+
+int kvm_s390_vcpu_setup_cmma(struct kvm_vcpu *vcpu)
+{
+	vcpu->arch.sie_block->cbrlo = get_zeroed_page(GFP_KERNEL);
+	if (!vcpu->arch.sie_block->cbrlo)
+		return -ENOMEM;
+
+	vcpu->arch.sie_block->ecb2 |= 0x80;
+	vcpu->arch.sie_block->ecb2 &= ~0x08;
+	return 0;
+}
+
 int kvm_arch_vcpu_setup(struct kvm_vcpu *vcpu)
 {
-	struct page *cbrl;
+	int rc = 0;
 
 	atomic_set(&vcpu->arch.sie_block->cpuflags, CPUSTAT_ZARCH |
 						    CPUSTAT_SM |
@@ -569,13 +585,10 @@ int kvm_arch_vcpu_setup(struct kvm_vcpu *vcpu)
 	vcpu->arch.sie_block->eca   = 0xC1002001U;
 	vcpu->arch.sie_block->fac   = (int) (long) vfacilities;
 	vcpu->arch.sie_block->ictl |= ICTL_ISKE | ICTL_SSKE | ICTL_RRBE;
-	if (kvm_enabled_cmma()) {
-		cbrl = alloc_page(GFP_KERNEL | __GFP_ZERO);
-		if (cbrl) {
-			vcpu->arch.sie_block->ecb2 |= 0x80;
-			vcpu->arch.sie_block->ecb2 &= ~0x08;
-			vcpu->arch.sie_block->cbrlo = page_to_phys(cbrl);
-		}
+	if (kvm_s390_cmma_enabled(vcpu->kvm)) {
+		rc = kvm_s390_vcpu_setup_cmma(vcpu);
+		if (rc)
+			return rc;
 	}
 	hrtimer_init(&vcpu->arch.ckc_timer, CLOCK_REALTIME, HRTIMER_MODE_ABS);
 	tasklet_init(&vcpu->arch.tasklet, kvm_s390_tasklet,
@@ -583,7 +596,7 @@ int kvm_arch_vcpu_setup(struct kvm_vcpu *vcpu)
 	vcpu->arch.ckc_timer.function = kvm_s390_idle_wakeup;
 	get_cpu_id(&vcpu->arch.cpu_id);
 	vcpu->arch.cpu_id.version = 0xff;
-	return 0;
+	return rc;
 }
 
 struct kvm_vcpu *kvm_arch_vcpu_create(struct kvm *kvm,
@@ -890,6 +903,18 @@ int kvm_arch_vcpu_ioctl_set_mpstate(struct kvm_vcpu *vcpu,
 	return -EINVAL; /* not implemented yet */
 }
 
+bool kvm_s390_cmma_enabled(struct kvm *kvm)
+{
+	if (!MACHINE_IS_LPAR)
+		return false;
+	/* only enable for z10 and later */
+	if (!MACHINE_HAS_EDAT1)
+		return false;
+	if (!kvm->arch.use_cmma)
+		return false;
+	return true;
+}
+
 static int kvm_s390_handle_requests(struct kvm_vcpu *vcpu)
 {
 	/*
@@ -1072,16 +1097,6 @@ static int vcpu_post_run(struct kvm_vcpu *vcpu, int exit_reason)
 	return rc;
 }
 
-bool kvm_enabled_cmma(void)
-{
-	if (!MACHINE_IS_LPAR)
-		return false;
-	/* only enable for z10 and later */
-	if (!MACHINE_HAS_EDAT1)
-		return false;
-	return true;
-}
-
 static int __vcpu_run(struct kvm_vcpu *vcpu)
 {
 	int rc, exit_reason;