KVM: s390: CMMA tracking, ESSA emulation, migration mode

* Add a migration state bitmap to keep track of which pages have dirty
  CMMA information.
* Disable CMMA by default, so we can track if it's used or not. Enable
  it on first use like we do for storage keys (unless we are doing a
  migration).
* Creates a VM attribute to enter and leave migration mode.
* In migration mode, CMMA is disabled in the SIE block, so ESSA is
  always interpreted and emulated in software.
* Free the migration state on VM destroy.

Signed-off-by: Claudio Imbrenda <[email protected]>
Acked-by: Cornelia Huck <[email protected]>
Reviewed-by: Christian Borntraeger <[email protected]>
Signed-off-by: Christian Borntraeger <[email protected]>

Documentation/virtual/kvm/devices/vm.txt

@@ -222,3 +222,36 @@ Allows user space to disable dea key wrapping, clearing the wrapping key.
 
 Parameters: none
 Returns:    0
+
+5. GROUP: KVM_S390_VM_MIGRATION
+Architectures: s390
+
+5.1. ATTRIBUTE: KVM_S390_VM_MIGRATION_STOP (w/o)
+
+Allows userspace to stop migration mode, needed for PGSTE migration.
+Setting this attribute when migration mode is not active will have no
+effects.
+
+Parameters: none
+Returns:    0
+
+5.2. ATTRIBUTE: KVM_S390_VM_MIGRATION_START (w/o)
+
+Allows userspace to start migration mode, needed for PGSTE migration.
+Setting this attribute when migration mode is already active will have
+no effects.
+
+Parameters: none
+Returns:    -ENOMEM if there is not enough free memory to start migration mode
+	    -EINVAL if the state of the VM is invalid (e.g. no memory defined)
+	    0 in case of success.
+
+5.3. ATTRIBUTE: KVM_S390_VM_MIGRATION_STATUS (r/o)
+
+Allows userspace to query the status of migration mode.
+
+Parameters: address of a buffer in user space to store the data (u64) to;
+	    the data itself is either 0 if migration mode is disabled or 1
+	    if it is enabled
+Returns:    -EFAULT if the given address is not accessible from kernel space
+	    0 in case of success.

arch/s390/include/asm/kvm_host.h

@@ -45,6 +45,8 @@
 #define KVM_REQ_ENABLE_IBS         8
 #define KVM_REQ_DISABLE_IBS        9
 #define KVM_REQ_ICPT_OPEREXC       10
+#define KVM_REQ_START_MIGRATION   11
+#define KVM_REQ_STOP_MIGRATION    12
 
 #define SIGP_CTRL_C		0x80
 #define SIGP_CTRL_SCN_MASK	0x3f
@@ -691,6 +693,12 @@ struct kvm_s390_vsie {
 	struct page *pages[KVM_MAX_VCPUS];
 };
 
+struct kvm_s390_migration_state {
+	unsigned long bitmap_size;	/* in bits (number of guest pages) */
+	atomic64_t dirty_pages;		/* number of dirty pages */
+	unsigned long *pgste_bitmap;
+};
+
 struct kvm_arch{
 	void *sca;
 	int use_esca;
@@ -718,6 +726,7 @@ struct kvm_arch{
 	struct kvm_s390_crypto crypto;
 	struct kvm_s390_vsie vsie;
 	u64 epoch;
+	struct kvm_s390_migration_state *migration_state;
 	/* subset of available cpu features enabled by user space */
 	DECLARE_BITMAP(cpu_feat, KVM_S390_VM_CPU_FEAT_NR_BITS);
 };

arch/s390/include/uapi/asm/kvm.h

@@ -70,6 +70,7 @@ struct kvm_s390_io_adapter_req {
 #define KVM_S390_VM_TOD			1
 #define KVM_S390_VM_CRYPTO		2
 #define KVM_S390_VM_CPU_MODEL		3
+#define KVM_S390_VM_MIGRATION		4
 
 /* kvm attributes for mem_ctrl */
 #define KVM_S390_VM_MEM_ENABLE_CMMA	0
@@ -151,6 +152,11 @@ struct kvm_s390_vm_cpu_subfunc {
 #define KVM_S390_VM_CRYPTO_DISABLE_AES_KW	2
 #define KVM_S390_VM_CRYPTO_DISABLE_DEA_KW	3
 
+/* kvm attributes for migration mode */
+#define KVM_S390_VM_MIGRATION_STOP	0
+#define KVM_S390_VM_MIGRATION_START	1
+#define KVM_S390_VM_MIGRATION_STATUS	2
+
 /* for KVM_GET_REGS and KVM_SET_REGS */
 struct kvm_regs {
 	/* general purpose regs for s390 */

arch/s390/kvm/kvm-s390.c

@@ -31,6 +31,7 @@
 #include <linux/bitmap.h>
 #include <linux/sched/signal.h>
 
+#include <linux/string.h>
 #include <asm/asm-offsets.h>
 #include <asm/lowcore.h>
 #include <asm/stp.h>
@@ -750,6 +751,129 @@ static int kvm_s390_vm_set_crypto(struct kvm *kvm, struct kvm_device_attr *attr)
 	return 0;
 }
 
+static void kvm_s390_sync_request_broadcast(struct kvm *kvm, int req)
+{
+	int cx;
+	struct kvm_vcpu *vcpu;
+
+	kvm_for_each_vcpu(cx, vcpu, kvm)
+		kvm_s390_sync_request(req, vcpu);
+}
+
+/*
+ * Must be called with kvm->srcu held to avoid races on memslots, and with
+ * kvm->lock to avoid races with ourselves and kvm_s390_vm_stop_migration.
+ */
+static int kvm_s390_vm_start_migration(struct kvm *kvm)
+{
+	struct kvm_s390_migration_state *mgs;
+	struct kvm_memory_slot *ms;
+	/* should be the only one */
+	struct kvm_memslots *slots;
+	unsigned long ram_pages;
+	int slotnr;
+
+	/* migration mode already enabled */
+	if (kvm->arch.migration_state)
+		return 0;
+
+	slots = kvm_memslots(kvm);
+	if (!slots || !slots->used_slots)
+		return -EINVAL;
+
+	mgs = kzalloc(sizeof(*mgs), GFP_KERNEL);
+	if (!mgs)
+		return -ENOMEM;
+	kvm->arch.migration_state = mgs;
+
+	if (kvm->arch.use_cmma) {
+		/*
+		 * Get the last slot. They should be sorted by base_gfn, so the
+		 * last slot is also the one at the end of the address space.
+		 * We have verified above that at least one slot is present.
+		 */
+		ms = slots->memslots + slots->used_slots - 1;
+		/* round up so we only use full longs */
+		ram_pages = roundup(ms->base_gfn + ms->npages, BITS_PER_LONG);
+		/* allocate enough bytes to store all the bits */
+		mgs->pgste_bitmap = vmalloc(ram_pages / 8);
+		if (!mgs->pgste_bitmap) {
+			kfree(mgs);
+			kvm->arch.migration_state = NULL;
+			return -ENOMEM;
+		}
+
+		mgs->bitmap_size = ram_pages;
+		atomic64_set(&mgs->dirty_pages, ram_pages);
+		/* mark all the pages in active slots as dirty */
+		for (slotnr = 0; slotnr < slots->used_slots; slotnr++) {
+			ms = slots->memslots + slotnr;
+			bitmap_set(mgs->pgste_bitmap, ms->base_gfn, ms->npages);
+		}
+
+		kvm_s390_sync_request_broadcast(kvm, KVM_REQ_START_MIGRATION);
+	}
+	return 0;
+}
+
+/*
+ * Must be called with kvm->lock to avoid races with ourselves and
+ * kvm_s390_vm_start_migration.
+ */
+static int kvm_s390_vm_stop_migration(struct kvm *kvm)
+{
+	struct kvm_s390_migration_state *mgs;
+
+	/* migration mode already disabled */
+	if (!kvm->arch.migration_state)
+		return 0;
+	mgs = kvm->arch.migration_state;
+	kvm->arch.migration_state = NULL;
+
+	if (kvm->arch.use_cmma) {
+		kvm_s390_sync_request_broadcast(kvm, KVM_REQ_STOP_MIGRATION);
+		vfree(mgs->pgste_bitmap);
+	}
+	kfree(mgs);
+	return 0;
+}
+
+static int kvm_s390_vm_set_migration(struct kvm *kvm,
+				     struct kvm_device_attr *attr)
+{
+	int idx, res = -ENXIO;
+
+	mutex_lock(&kvm->lock);
+	switch (attr->attr) {
+	case KVM_S390_VM_MIGRATION_START:
+		idx = srcu_read_lock(&kvm->srcu);
+		res = kvm_s390_vm_start_migration(kvm);
+		srcu_read_unlock(&kvm->srcu, idx);
+		break;
+	case KVM_S390_VM_MIGRATION_STOP:
+		res = kvm_s390_vm_stop_migration(kvm);
+		break;
+	default:
+		break;
+	}
+	mutex_unlock(&kvm->lock);
+
+	return res;
+}
+
+static int kvm_s390_vm_get_migration(struct kvm *kvm,
+				     struct kvm_device_attr *attr)
+{
+	u64 mig = (kvm->arch.migration_state != NULL);
+
+	if (attr->attr != KVM_S390_VM_MIGRATION_STATUS)
+		return -ENXIO;
+
+	if (copy_to_user((void __user *)attr->addr, &mig, sizeof(mig)))
+		return -EFAULT;
+	return 0;
+}
+
 static int kvm_s390_set_tod_high(struct kvm *kvm, struct kvm_device_attr *attr)
 {
 	u8 gtod_high;
@@ -1090,6 +1214,9 @@ static int kvm_s390_vm_set_attr(struct kvm *kvm, struct kvm_device_attr *attr)
 	case KVM_S390_VM_CRYPTO:
 		ret = kvm_s390_vm_set_crypto(kvm, attr);
 		break;
+	case KVM_S390_VM_MIGRATION:
+		ret = kvm_s390_vm_set_migration(kvm, attr);
+		break;
 	default:
 		ret = -ENXIO;
 		break;
@@ -1112,6 +1239,9 @@ static int kvm_s390_vm_get_attr(struct kvm *kvm, struct kvm_device_attr *attr)
 	case KVM_S390_VM_CPU_MODEL:
 		ret = kvm_s390_get_cpu_model(kvm, attr);
 		break;
+	case KVM_S390_VM_MIGRATION:
+		ret = kvm_s390_vm_get_migration(kvm, attr);
+		break;
 	default:
 		ret = -ENXIO;
 		break;
@@ -1179,6 +1309,9 @@ static int kvm_s390_vm_has_attr(struct kvm *kvm, struct kvm_device_attr *attr)
 			break;
 		}
 		break;
+	case KVM_S390_VM_MIGRATION:
+		ret = 0;
+		break;
 	default:
 		ret = -ENXIO;
 		break;
@@ -1633,6 +1766,10 @@ void kvm_arch_destroy_vm(struct kvm *kvm)
 	kvm_s390_destroy_adapters(kvm);
 	kvm_s390_clear_float_irqs(kvm);
 	kvm_s390_vsie_destroy(kvm);
+	if (kvm->arch.migration_state) {
+		vfree(kvm->arch.migration_state->pgste_bitmap);
+		kfree(kvm->arch.migration_state);
+	}
 	KVM_EVENT(3, "vm 0x%pK destroyed", kvm);
 }
 
@@ -1977,7 +2114,6 @@ int kvm_s390_vcpu_setup_cmma(struct kvm_vcpu *vcpu)
 	if (!vcpu->arch.sie_block->cbrlo)
 		return -ENOMEM;
 
-	vcpu->arch.sie_block->ecb2 |= ECB2_CMMA;
 	vcpu->arch.sie_block->ecb2 &= ~ECB2_PFMFI;
 	return 0;
 }
@@ -2489,6 +2625,27 @@ static int kvm_s390_handle_requests(struct kvm_vcpu *vcpu)
 		goto retry;
 	}
 
+	if (kvm_check_request(KVM_REQ_START_MIGRATION, vcpu)) {
+		/*
+		 * Disable CMMA virtualization; we will emulate the ESSA
+		 * instruction manually, in order to provide additional
+		 * functionalities needed for live migration.
+		 */
+		vcpu->arch.sie_block->ecb2 &= ~ECB2_CMMA;
+		goto retry;
+	}
+
+	if (kvm_check_request(KVM_REQ_STOP_MIGRATION, vcpu)) {
+		/*
+		 * Re-enable CMMA virtualization if CMMA is available and
+		 * was used.
+		 */
+		if ((vcpu->kvm->arch.use_cmma) &&
+		    (vcpu->kvm->mm->context.use_cmma))
+			vcpu->arch.sie_block->ecb2 |= ECB2_CMMA;
+		goto retry;
+	}
+
 	/* nothing to do, just clear the request */
 	kvm_clear_request(KVM_REQ_UNHALT, vcpu);