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 <[e-mail]>
Acked-by: Cornelia Huck <[e-mail]>
Reviewed-by: Christian Borntraeger <[e-mail]>
Signed-off-by: Christian Borntraeger <[e-mail]>

Documentation/virtual/kvm/devices/vm.txt

···
 
 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

···
 #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
···
 	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;
···
 	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

···
 #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
···
 #define KVM_S390_VM_CRYPTO_ENABLE_DEA_KW	1
 #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 {

arch/s390/kvm/kvm-s390.c

···
 #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>
···
 	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;
···
 	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;
···
 		break;
 	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;
···
 			ret = -ENXIO;
 			break;
 		}
+		break;
+	case KVM_S390_VM_MIGRATION:
+		ret = 0;
 		break;
 	default:
 		ret = -ENXIO;
···
 	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);
 }
 
···
 	if (!vcpu->arch.sie_block->cbrlo)
 		return -ENOMEM;
 
-	vcpu->arch.sie_block->ecb2 |= ECB2_CMMA;
 	vcpu->arch.sie_block->ecb2 &= ~ECB2_PFMFI;
 	return 0;
 }
···
 
 	if (kvm_check_request(KVM_REQ_ICPT_OPEREXC, vcpu)) {
 		vcpu->arch.sie_block->ictl |= ICTL_OPEREXC;
+		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;
 	}
 

arch/s390/kvm/priv.c

···
 #include <asm/ebcdic.h>
 #include <asm/sysinfo.h>
 #include <asm/pgtable.h>
+#include <asm/page-states.h>
 #include <asm/pgalloc.h>
 #include <asm/gmap.h>
 #include <asm/io.h>
···
 	return 0;
 }
 
+static inline int do_essa(struct kvm_vcpu *vcpu, const int orc)
+{
+	struct kvm_s390_migration_state *ms = vcpu->kvm->arch.migration_state;
+	int r1, r2, nappended, entries;
+	unsigned long gfn, hva, res, pgstev, ptev;
+	unsigned long *cbrlo;
+
+	/*
+	 * We don't need to set SD.FPF.SK to 1 here, because if we have a
+	 * machine check here we either handle it or crash
+	 */
+
+	kvm_s390_get_regs_rre(vcpu, &r1, &r2);
+	gfn = vcpu->run->s.regs.gprs[r2] >> PAGE_SHIFT;
+	hva = gfn_to_hva(vcpu->kvm, gfn);
+	entries = (vcpu->arch.sie_block->cbrlo & ~PAGE_MASK) >> 3;
+
+	if (kvm_is_error_hva(hva))
+		return kvm_s390_inject_program_int(vcpu, PGM_ADDRESSING);
+
+	nappended = pgste_perform_essa(vcpu->kvm->mm, hva, orc, &ptev, &pgstev);
+	if (nappended < 0) {
+		res = orc ? 0x10 : 0;
+		vcpu->run->s.regs.gprs[r1] = res; /* Exception Indication */
+		return 0;
+	}
+	res = (pgstev & _PGSTE_GPS_USAGE_MASK) >> 22;
+	/*
+	 * Set the block-content state part of the result. 0 means resident, so
+	 * nothing to do if the page is valid. 2 is for preserved pages
+	 * (non-present and non-zero), and 3 for zero pages (non-present and
+	 * zero).
+	 */
+	if (ptev & _PAGE_INVALID) {
+		res |= 2;
+		if (pgstev & _PGSTE_GPS_ZERO)
+			res |= 1;
+	}
+	vcpu->run->s.regs.gprs[r1] = res;
+	/*
+	 * It is possible that all the normal 511 slots were full, in which case
+	 * we will now write in the 512th slot, which is reserved for host use.
+	 * In both cases we let the normal essa handling code process all the
+	 * slots, including the reserved one, if needed.
+	 */
+	if (nappended > 0) {
+		cbrlo = phys_to_virt(vcpu->arch.sie_block->cbrlo & PAGE_MASK);
+		cbrlo[entries] = gfn << PAGE_SHIFT;
+	}
+
+	if (orc) {
+		/* increment only if we are really flipping the bit to 1 */
+		if (!test_and_set_bit(gfn, ms->pgste_bitmap))
+			atomic64_inc(&ms->dirty_pages);
+	}
+
+	return nappended;
+}
+
 static int handle_essa(struct kvm_vcpu *vcpu)
 {
 	/* entries expected to be 1FF */
 	int entries = (vcpu->arch.sie_block->cbrlo & ~PAGE_MASK) >> 3;
 	unsigned long *cbrlo;
 	struct gmap *gmap;
-	int i;
+	int i, orc;
 
 	VCPU_EVENT(vcpu, 4, "ESSA: release %d pages", entries);
 	gmap = vcpu->arch.gmap;
···
 
 	if (vcpu->arch.sie_block->gpsw.mask & PSW_MASK_PSTATE)
 		return kvm_s390_inject_program_int(vcpu, PGM_PRIVILEGED_OP);
-
-	if (((vcpu->arch.sie_block->ipb & 0xf0000000) >> 28) > 6)
+	/* Check for invalid operation request code */
+	orc = (vcpu->arch.sie_block->ipb & 0xf0000000) >> 28;
+	if (orc > ESSA_MAX)
 		return kvm_s390_inject_program_int(vcpu, PGM_SPECIFICATION);
 
-	/* Retry the ESSA instruction */
-	kvm_s390_retry_instr(vcpu);
+	if (likely(!vcpu->kvm->arch.migration_state)) {
+		/*
+		 * CMMA is enabled in the KVM settings, but is disabled in
+		 * the SIE block and in the mm_context, and we are not doing
+		 * a migration. Enable CMMA in the mm_context.
+		 * Since we need to take a write lock to write to the context
+		 * to avoid races with storage keys handling, we check if the
+		 * value really needs to be written to; if the value is
+		 * already correct, we do nothing and avoid the lock.
+		 */
+		if (vcpu->kvm->mm->context.use_cmma == 0) {
+			down_write(&vcpu->kvm->mm->mmap_sem);
+			vcpu->kvm->mm->context.use_cmma = 1;
+			up_write(&vcpu->kvm->mm->mmap_sem);
+		}
+		/*
+		 * If we are here, we are supposed to have CMMA enabled in
+		 * the SIE block. Enabling CMMA works on a per-CPU basis,
+		 * while the context use_cmma flag is per process.
+		 * It's possible that the context flag is enabled and the
+		 * SIE flag is not, so we set the flag always; if it was
+		 * already set, nothing changes, otherwise we enable it
+		 * on this CPU too.
+		 */
+		vcpu->arch.sie_block->ecb2 |= ECB2_CMMA;
+		/* Retry the ESSA instruction */
+		kvm_s390_retry_instr(vcpu);
+	} else {
+		/* Account for the possible extra cbrl entry */
+		i = do_essa(vcpu, orc);
+		if (i < 0)
+			return i;
+		entries += i;
+	}
 	vcpu->arch.sie_block->cbrlo &= PAGE_MASK;	/* reset nceo */
 	cbrlo = phys_to_virt(vcpu->arch.sie_block->cbrlo);
 	down_read(&gmap->mm->mmap_sem);