diff --git a/arch/ia64/include/asm/kvm_host.h b/arch/ia64/include/asm/kvm_host.h
index c4b4bac..6d6a5ac 100644
--- a/arch/ia64/include/asm/kvm_host.h
+++ b/arch/ia64/include/asm/kvm_host.h
@@ -449,6 +449,8 @@
 	char log_buf[VMM_LOG_LEN];
 	union context host;
 	union context guest;
+
+	char mmio_data[8];
 };
 
 struct kvm_vm_stat {
diff --git a/arch/ia64/kvm/kvm-ia64.c b/arch/ia64/kvm/kvm-ia64.c
index 9d80ff8..882ab21 100644
--- a/arch/ia64/kvm/kvm-ia64.c
+++ b/arch/ia64/kvm/kvm-ia64.c
@@ -232,12 +232,12 @@
 	if ((p->addr & PAGE_MASK) == IOAPIC_DEFAULT_BASE_ADDRESS)
 		goto mmio;
 	vcpu->mmio_needed = 1;
-	vcpu->mmio_phys_addr = kvm_run->mmio.phys_addr = p->addr;
-	vcpu->mmio_size = kvm_run->mmio.len = p->size;
+	vcpu->mmio_fragments[0].gpa = kvm_run->mmio.phys_addr = p->addr;
+	vcpu->mmio_fragments[0].len = kvm_run->mmio.len = p->size;
 	vcpu->mmio_is_write = kvm_run->mmio.is_write = !p->dir;
 
 	if (vcpu->mmio_is_write)
-		memcpy(vcpu->mmio_data, &p->data, p->size);
+		memcpy(vcpu->arch.mmio_data, &p->data, p->size);
 	memcpy(kvm_run->mmio.data, &p->data, p->size);
 	kvm_run->exit_reason = KVM_EXIT_MMIO;
 	return 0;
@@ -719,7 +719,7 @@
 	struct kvm_mmio_req *p = kvm_get_vcpu_ioreq(vcpu);
 
 	if (!vcpu->mmio_is_write)
-		memcpy(&p->data, vcpu->mmio_data, 8);
+		memcpy(&p->data, vcpu->arch.mmio_data, 8);
 	p->state = STATE_IORESP_READY;
 }
 
@@ -739,7 +739,7 @@
 	}
 
 	if (vcpu->mmio_needed) {
-		memcpy(vcpu->mmio_data, kvm_run->mmio.data, 8);
+		memcpy(vcpu->arch.mmio_data, kvm_run->mmio.data, 8);
 		kvm_set_mmio_data(vcpu);
 		vcpu->mmio_read_completed = 1;
 		vcpu->mmio_needed = 0;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 0d9a578..4de705c 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3718,9 +3718,8 @@
 static int read_prepare(struct kvm_vcpu *vcpu, void *val, int bytes)
 {
 	if (vcpu->mmio_read_completed) {
-		memcpy(val, vcpu->mmio_data, bytes);
 		trace_kvm_mmio(KVM_TRACE_MMIO_READ, bytes,
-			       vcpu->mmio_phys_addr, *(u64 *)val);
+			       vcpu->mmio_fragments[0].gpa, *(u64 *)val);
 		vcpu->mmio_read_completed = 0;
 		return 1;
 	}
@@ -3756,8 +3755,9 @@
 static int write_exit_mmio(struct kvm_vcpu *vcpu, gpa_t gpa,
 			   void *val, int bytes)
 {
-	memcpy(vcpu->mmio_data, val, bytes);
-	memcpy(vcpu->run->mmio.data, vcpu->mmio_data, 8);
+	struct kvm_mmio_fragment *frag = &vcpu->mmio_fragments[0];
+
+	memcpy(vcpu->run->mmio.data, frag->data, frag->len);
 	return X86EMUL_CONTINUE;
 }
 
@@ -3784,10 +3784,7 @@
 	gpa_t gpa;
 	int handled, ret;
 	bool write = ops->write;
-
-	if (ops->read_write_prepare &&
-		  ops->read_write_prepare(vcpu, val, bytes))
-		return X86EMUL_CONTINUE;
+	struct kvm_mmio_fragment *frag;
 
 	ret = vcpu_mmio_gva_to_gpa(vcpu, addr, &gpa, exception, write);
 
@@ -3813,15 +3810,19 @@
 	bytes -= handled;
 	val += handled;
 
-	vcpu->mmio_needed = 1;
-	vcpu->run->exit_reason = KVM_EXIT_MMIO;
-	vcpu->run->mmio.phys_addr = vcpu->mmio_phys_addr = gpa;
-	vcpu->mmio_size = bytes;
-	vcpu->run->mmio.len = min(vcpu->mmio_size, 8);
-	vcpu->run->mmio.is_write = vcpu->mmio_is_write = write;
-	vcpu->mmio_index = 0;
+	while (bytes) {
+		unsigned now = min(bytes, 8U);
 
-	return ops->read_write_exit_mmio(vcpu, gpa, val, bytes);
+		frag = &vcpu->mmio_fragments[vcpu->mmio_nr_fragments++];
+		frag->gpa = gpa;
+		frag->data = val;
+		frag->len = now;
+
+		gpa += now;
+		val += now;
+		bytes -= now;
+	}
+	return X86EMUL_CONTINUE;
 }
 
 int emulator_read_write(struct x86_emulate_ctxt *ctxt, unsigned long addr,
@@ -3830,10 +3831,18 @@
 			struct read_write_emulator_ops *ops)
 {
 	struct kvm_vcpu *vcpu = emul_to_vcpu(ctxt);
+	gpa_t gpa;
+	int rc;
+
+	if (ops->read_write_prepare &&
+		  ops->read_write_prepare(vcpu, val, bytes))
+		return X86EMUL_CONTINUE;
+
+	vcpu->mmio_nr_fragments = 0;
 
 	/* Crossing a page boundary? */
 	if (((addr + bytes - 1) ^ addr) & PAGE_MASK) {
-		int rc, now;
+		int now;
 
 		now = -addr & ~PAGE_MASK;
 		rc = emulator_read_write_onepage(addr, val, now, exception,
@@ -3846,8 +3855,25 @@
 		bytes -= now;
 	}
 
-	return emulator_read_write_onepage(addr, val, bytes, exception,
-					   vcpu, ops);
+	rc = emulator_read_write_onepage(addr, val, bytes, exception,
+					 vcpu, ops);
+	if (rc != X86EMUL_CONTINUE)
+		return rc;
+
+	if (!vcpu->mmio_nr_fragments)
+		return rc;
+
+	gpa = vcpu->mmio_fragments[0].gpa;
+
+	vcpu->mmio_needed = 1;
+	vcpu->mmio_cur_fragment = 0;
+
+	vcpu->run->mmio.len = vcpu->mmio_fragments[0].len;
+	vcpu->run->mmio.is_write = vcpu->mmio_is_write = ops->write;
+	vcpu->run->exit_reason = KVM_EXIT_MMIO;
+	vcpu->run->mmio.phys_addr = gpa;
+
+	return ops->read_write_exit_mmio(vcpu, gpa, val, bytes);
 }
 
 static int emulator_read_emulated(struct x86_emulate_ctxt *ctxt,
@@ -5446,33 +5472,55 @@
 	return r;
 }
 
+/*
+ * Implements the following, as a state machine:
+ *
+ * read:
+ *   for each fragment
+ *     write gpa, len
+ *     exit
+ *     copy data
+ *   execute insn
+ *
+ * write:
+ *   for each fragment
+ *      write gpa, len
+ *      copy data
+ *      exit
+ */
 static int complete_mmio(struct kvm_vcpu *vcpu)
 {
 	struct kvm_run *run = vcpu->run;
+	struct kvm_mmio_fragment *frag;
 	int r;
 
 	if (!(vcpu->arch.pio.count || vcpu->mmio_needed))
 		return 1;
 
 	if (vcpu->mmio_needed) {
-		vcpu->mmio_needed = 0;
+		/* Complete previous fragment */
+		frag = &vcpu->mmio_fragments[vcpu->mmio_cur_fragment++];
 		if (!vcpu->mmio_is_write)
-			memcpy(vcpu->mmio_data + vcpu->mmio_index,
-			       run->mmio.data, 8);
-		vcpu->mmio_index += 8;
-		if (vcpu->mmio_index < vcpu->mmio_size) {
-			run->exit_reason = KVM_EXIT_MMIO;
-			run->mmio.phys_addr = vcpu->mmio_phys_addr + vcpu->mmio_index;
-			memcpy(run->mmio.data, vcpu->mmio_data + vcpu->mmio_index, 8);
-			run->mmio.len = min(vcpu->mmio_size - vcpu->mmio_index, 8);
-			run->mmio.is_write = vcpu->mmio_is_write;
-			vcpu->mmio_needed = 1;
-			return 0;
+			memcpy(frag->data, run->mmio.data, frag->len);
+		if (vcpu->mmio_cur_fragment == vcpu->mmio_nr_fragments) {
+			vcpu->mmio_needed = 0;
+			if (vcpu->mmio_is_write)
+				return 1;
+			vcpu->mmio_read_completed = 1;
+			goto done;
 		}
+		/* Initiate next fragment */
+		++frag;
+		run->exit_reason = KVM_EXIT_MMIO;
+		run->mmio.phys_addr = frag->gpa;
 		if (vcpu->mmio_is_write)
-			return 1;
-		vcpu->mmio_read_completed = 1;
+			memcpy(run->mmio.data, frag->data, frag->len);
+		run->mmio.len = frag->len;
+		run->mmio.is_write = vcpu->mmio_is_write;
+		return 0;
+
 	}
+done:
 	vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
 	r = emulate_instruction(vcpu, EMULTYPE_NO_DECODE);
 	srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index a2d00b1..186ffab 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -35,6 +35,20 @@
 #endif
 
 /*
+ * If we support unaligned MMIO, at most one fragment will be split into two:
+ */
+#ifdef KVM_UNALIGNED_MMIO
+#  define KVM_EXTRA_MMIO_FRAGMENTS 1
+#else
+#  define KVM_EXTRA_MMIO_FRAGMENTS 0
+#endif
+
+#define KVM_USER_MMIO_SIZE 8
+
+#define KVM_MAX_MMIO_FRAGMENTS \
+	(KVM_MMIO_SIZE / KVM_USER_MMIO_SIZE + KVM_EXTRA_MMIO_FRAGMENTS)
+
+/*
  * vcpu->requests bit members
  */
 #define KVM_REQ_TLB_FLUSH          0
@@ -117,6 +131,16 @@
 	EXITING_GUEST_MODE
 };
 
+/*
+ * Sometimes a large or cross-page mmio needs to be broken up into separate
+ * exits for userspace servicing.
+ */
+struct kvm_mmio_fragment {
+	gpa_t gpa;
+	void *data;
+	unsigned len;
+};
+
 struct kvm_vcpu {
 	struct kvm *kvm;
 #ifdef CONFIG_PREEMPT_NOTIFIERS
@@ -144,10 +168,9 @@
 	int mmio_needed;
 	int mmio_read_completed;
 	int mmio_is_write;
-	int mmio_size;
-	int mmio_index;
-	unsigned char mmio_data[KVM_MMIO_SIZE];
-	gpa_t mmio_phys_addr;
+	int mmio_cur_fragment;
+	int mmio_nr_fragments;
+	struct kvm_mmio_fragment mmio_fragments[KVM_MAX_MMIO_FRAGMENTS];
 #endif
 
 #ifdef CONFIG_KVM_ASYNC_PF