diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index 683bc619aa..a008d7df1c 100644
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -2211,6 +2211,19 @@ int domain_relinquish_resources(struct domain *d)
             ret = relinquish_shared_pages(d);
             if ( ret )
                 return ret;
+
+            /*
+             * If the domain is forked, decrement the parent's pause count
+             * and release the domain.
+             */
+            if ( mem_sharing_is_fork(d) )
+            {
+                struct domain *parent = d->parent;
+
+                d->parent = NULL;
+                domain_unpause(parent);
+                put_domain(parent);
+            }
         }
 #endif
 
diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index a3d115b650..304b3d1562 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -1917,7 +1917,7 @@ int hvm_hap_nested_page_fault(paddr_t gpa, unsigned long gla,
     }
 #endif
 
-    /* Spurious fault? PoD and log-dirty also take this path. */
+    /* Spurious fault? PoD, log-dirty and VM forking also take this path. */
     if ( p2m_is_ram(p2mt) )
     {
         rc = 1;
@@ -4377,7 +4377,7 @@ static int hvm_allow_get_param(struct domain *d,
     return rc;
 }
 
-static int hvm_get_param(struct domain *d, uint32_t index, uint64_t *value)
+int hvm_get_param(struct domain *d, uint32_t index, uint64_t *value)
 {
     int rc;
 
diff --git a/xen/arch/x86/mm/hap/hap.c b/xen/arch/x86/mm/hap/hap.c
index a6d5e39b02..814d0c3253 100644
--- a/xen/arch/x86/mm/hap/hap.c
+++ b/xen/arch/x86/mm/hap/hap.c
@@ -321,8 +321,7 @@ static void hap_free_p2m_page(struct domain *d, struct page_info *pg)
 }
 
 /* Return the size of the pool, rounded up to the nearest MB */
-static unsigned int
-hap_get_allocation(struct domain *d)
+unsigned int hap_get_allocation(struct domain *d)
 {
     unsigned int pg = d->arch.paging.hap.total_pages
         + d->arch.paging.hap.p2m_pages;
diff --git a/xen/arch/x86/mm/mem_sharing.c b/xen/arch/x86/mm/mem_sharing.c
index f49f27a3ef..faa79011c3 100644
--- a/xen/arch/x86/mm/mem_sharing.c
+++ b/xen/arch/x86/mm/mem_sharing.c
@@ -22,6 +22,7 @@
 
 #include <xen/types.h>
 #include <xen/domain_page.h>
+#include <xen/event.h>
 #include <xen/spinlock.h>
 #include <xen/rwlock.h>
 #include <xen/mm.h>
@@ -36,6 +37,8 @@
 #include <asm/altp2m.h>
 #include <asm/atomic.h>
 #include <asm/event.h>
+#include <asm/hap.h>
+#include <asm/hvm/hvm.h>
 #include <xsm/xsm.h>
 
 #include "mm-locks.h"
@@ -1443,6 +1446,318 @@ static inline int mem_sharing_control(struct domain *d, bool enable)
     return 0;
 }
 
+/*
+ * Forking a page only gets called when the VM faults due to no entry being
+ * in the EPT for the access. Depending on the type of access we either
+ * populate the physmap with a shared entry for read-only access or
+ * fork the page if its a write access.
+ *
+ * The client p2m is already locked so we only need to lock
+ * the parent's here.
+ */
+int mem_sharing_fork_page(struct domain *d, gfn_t gfn, bool unsharing)
+{
+    int rc = -ENOENT;
+    shr_handle_t handle;
+    struct domain *parent = d->parent;
+    struct p2m_domain *p2m;
+    unsigned long gfn_l = gfn_x(gfn);
+    mfn_t mfn, new_mfn;
+    p2m_type_t p2mt;
+    struct page_info *page;
+
+    if ( !mem_sharing_is_fork(d) )
+        return -ENOENT;
+
+    if ( !unsharing )
+    {
+        /* For read-only accesses we just add a shared entry to the physmap */
+        while ( parent )
+        {
+            if ( !(rc = nominate_page(parent, gfn, 0, &handle)) )
+                break;
+
+            parent = parent->parent;
+        }
+
+        if ( !rc )
+        {
+            /* The client's p2m is already locked */
+            p2m = p2m_get_hostp2m(parent);
+
+            p2m_lock(p2m);
+            rc = add_to_physmap(parent, gfn_l, handle, d, gfn_l, false);
+            p2m_unlock(p2m);
+
+            if ( !rc )
+                return 0;
+        }
+    }
+
+    /*
+     * If it's a write access (ie. unsharing) or if adding a shared entry to
+     * the physmap failed we'll fork the page directly.
+     */
+    p2m = p2m_get_hostp2m(d);
+    parent = d->parent;
+
+    while ( parent )
+    {
+        mfn = get_gfn_query(parent, gfn_l, &p2mt);
+
+        /* We can't fork grant memory from the parent, only regular ram */
+        if ( mfn_valid(mfn) && p2m_is_ram(p2mt) )
+            break;
+
+        put_gfn(parent, gfn_l);
+        parent = parent->parent;
+    }
+
+    if ( !parent )
+        return -ENOENT;
+
+    if ( !(page = alloc_domheap_page(d, 0)) )
+    {
+        put_gfn(parent, gfn_l);
+        return -ENOMEM;
+    }
+
+    new_mfn = page_to_mfn(page);
+    copy_domain_page(new_mfn, mfn);
+    set_gpfn_from_mfn(mfn_x(new_mfn), gfn_l);
+
+    put_gfn(parent, gfn_l);
+
+    return p2m->set_entry(p2m, gfn, new_mfn, PAGE_ORDER_4K, p2m_ram_rw,
+                          p2m->default_access, -1);
+}
+
+static int bring_up_vcpus(struct domain *cd, struct domain *d)
+{
+    unsigned int i;
+    int ret = -EINVAL;
+
+    if ( d->max_vcpus != cd->max_vcpus ||
+        (ret = cpupool_move_domain(cd, d->cpupool)) )
+        return ret;
+
+    for ( i = 0; i < cd->max_vcpus; i++ )
+    {
+        if ( !d->vcpu[i] || cd->vcpu[i] )
+            continue;
+
+        if ( !vcpu_create(cd, i) )
+            return -EINVAL;
+    }
+
+    domain_update_node_affinity(cd);
+    return 0;
+}
+
+static int copy_vcpu_settings(struct domain *cd, struct domain *d)
+{
+    unsigned int i;
+    struct p2m_domain *p2m = p2m_get_hostp2m(cd);
+    int ret = -EINVAL;
+
+    for ( i = 0; i < cd->max_vcpus; i++ )
+    {
+        const struct vcpu *d_vcpu = d->vcpu[i];
+        struct vcpu *cd_vcpu = cd->vcpu[i];
+        struct vcpu_runstate_info runstate;
+        mfn_t vcpu_info_mfn;
+
+        if ( !d_vcpu || !cd_vcpu )
+            continue;
+
+        /* Copy & map in the vcpu_info page if the guest uses one */
+        vcpu_info_mfn = d_vcpu->vcpu_info_mfn;
+        if ( !mfn_eq(vcpu_info_mfn, INVALID_MFN) )
+        {
+            mfn_t new_vcpu_info_mfn = cd_vcpu->vcpu_info_mfn;
+
+            /* Allocate & map the page for it if it hasn't been already */
+            if ( mfn_eq(new_vcpu_info_mfn, INVALID_MFN) )
+            {
+                gfn_t gfn = mfn_to_gfn(d, vcpu_info_mfn);
+                unsigned long gfn_l = gfn_x(gfn);
+                struct page_info *page;
+
+                if ( !(page = alloc_domheap_page(cd, 0)) )
+                    return -ENOMEM;
+
+                new_vcpu_info_mfn = page_to_mfn(page);
+                set_gpfn_from_mfn(mfn_x(new_vcpu_info_mfn), gfn_l);
+
+                ret = p2m->set_entry(p2m, gfn, new_vcpu_info_mfn,
+                                     PAGE_ORDER_4K, p2m_ram_rw,
+                                     p2m->default_access, -1);
+                if ( ret )
+                    return ret;
+
+                ret = map_vcpu_info(cd_vcpu, gfn_l,
+                                    PAGE_OFFSET(d_vcpu->vcpu_info));
+                if ( ret )
+                    return ret;
+            }
+
+            copy_domain_page(new_vcpu_info_mfn, vcpu_info_mfn);
+        }
+
+        /* Setup the vCPU runstate area */
+        if ( !guest_handle_is_null(runstate_guest(d_vcpu)) )
+        {
+            runstate_guest(cd_vcpu) = runstate_guest(d_vcpu);
+            vcpu_runstate_get(cd_vcpu, &runstate);
+            __copy_to_guest(runstate_guest(cd_vcpu), &runstate, 1);
+        }
+
+        /*
+         * TODO: to support VMs with PV interfaces copy additional
+         * settings here, such as PV timers.
+         */
+    }
+
+    return 0;
+}
+
+static int fork_hap_allocation(struct domain *cd, struct domain *d)
+{
+    int rc;
+    bool preempted;
+    unsigned long mb = hap_get_allocation(d);
+
+    if ( mb == hap_get_allocation(cd) )
+        return 0;
+
+    paging_lock(cd);
+    rc = hap_set_allocation(cd, mb << (20 - PAGE_SHIFT), &preempted);
+    paging_unlock(cd);
+
+    return preempted ? -ERESTART : rc;
+}
+
+static void copy_tsc(struct domain *cd, struct domain *d)
+{
+    uint32_t tsc_mode;
+    uint32_t gtsc_khz;
+    uint32_t incarnation;
+    uint64_t elapsed_nsec;
+
+    tsc_get_info(d, &tsc_mode, &elapsed_nsec, &gtsc_khz, &incarnation);
+    /* Don't bump incarnation on set */
+    tsc_set_info(cd, tsc_mode, elapsed_nsec, gtsc_khz, incarnation - 1);
+}
+
+static int copy_special_pages(struct domain *cd, struct domain *d)
+{
+    mfn_t new_mfn, old_mfn;
+    struct p2m_domain *p2m = p2m_get_hostp2m(cd);
+    static const unsigned int params[] =
+    {
+        HVM_PARAM_STORE_PFN,
+        HVM_PARAM_IOREQ_PFN,
+        HVM_PARAM_BUFIOREQ_PFN,
+        HVM_PARAM_CONSOLE_PFN
+    };
+    unsigned int i;
+    int rc;
+
+    for ( i = 0; i < ARRAY_SIZE(params); i++ )
+    {
+        p2m_type_t t;
+        uint64_t value = 0;
+        struct page_info *page;
+
+        if ( hvm_get_param(cd, params[i], &value) || !value )
+            continue;
+
+        old_mfn = get_gfn_query_unlocked(d, value, &t);
+        new_mfn = get_gfn_query_unlocked(cd, value, &t);
+
+        /* Allocate the page and map it in if it's not present */
+        if ( mfn_eq(new_mfn, INVALID_MFN) )
+        {
+            if ( !(page = alloc_domheap_page(cd, 0)) )
+                return -ENOMEM;
+
+            new_mfn = page_to_mfn(page);
+            set_gpfn_from_mfn(mfn_x(new_mfn), value);
+
+            rc = p2m->set_entry(p2m, _gfn(value), new_mfn, PAGE_ORDER_4K,
+                                p2m_ram_rw, p2m->default_access, -1);
+            if ( rc )
+                return rc;
+        }
+
+        copy_domain_page(new_mfn, old_mfn);
+    }
+
+    old_mfn = _mfn(virt_to_mfn(d->shared_info));
+    new_mfn = _mfn(virt_to_mfn(cd->shared_info));
+    copy_domain_page(new_mfn, old_mfn);
+
+    return 0;
+}
+
+static int copy_settings(struct domain *cd, struct domain *d)
+{
+    int rc;
+
+    if ( (rc = copy_vcpu_settings(cd, d)) )
+        return rc;
+
+    if ( (rc = hvm_copy_context_and_params(cd, d)) )
+        return rc;
+
+    if ( (rc = copy_special_pages(cd, d)) )
+        return rc;
+
+    copy_tsc(cd, d);
+
+    return rc;
+}
+
+static int fork(struct domain *cd, struct domain *d)
+{
+    int rc = -EBUSY;
+
+    if ( !cd->controller_pause_count )
+        return rc;
+
+    if ( !cd->parent )
+    {
+        if ( !get_domain(d) )
+        {
+            ASSERT_UNREACHABLE();
+            return -EBUSY;
+        }
+
+        domain_pause(d);
+        cd->max_pages = d->max_pages;
+        cd->parent = d;
+    }
+
+    /* This is preemptible so it's the first to get done */
+    if ( (rc = fork_hap_allocation(cd, d)) )
+        goto done;
+
+    if ( (rc = bring_up_vcpus(cd, d)) )
+        goto done;
+
+    rc = copy_settings(cd, d);
+
+ done:
+    if ( rc && rc != -ERESTART )
+    {
+        domain_unpause(d);
+        put_domain(d);
+        cd->parent = NULL;
+    }
+
+    return rc;
+}
+
 int mem_sharing_memop(XEN_GUEST_HANDLE_PARAM(xen_mem_sharing_op_t) arg)
 {
     int rc;
@@ -1697,6 +2012,42 @@ int mem_sharing_memop(XEN_GUEST_HANDLE_PARAM(xen_mem_sharing_op_t) arg)
         rc = debug_gref(d, mso.u.debug.u.gref);
         break;
 
+    case XENMEM_sharing_op_fork:
+    {
+        struct domain *pd;
+
+        rc = -EINVAL;
+        if ( mso.u.fork.pad[0] || mso.u.fork.pad[1] || mso.u.fork.pad[2] )
+            goto out;
+
+        rc = rcu_lock_live_remote_domain_by_id(mso.u.fork.parent_domain,
+                                               &pd);
+        if ( rc )
+            goto out;
+
+        rc = -EINVAL;
+        if ( pd->max_vcpus != d->max_vcpus )
+        {
+            rcu_unlock_domain(pd);
+            goto out;
+        }
+
+        if ( !mem_sharing_enabled(pd) && (rc = mem_sharing_control(pd, true)) )
+        {
+            rcu_unlock_domain(pd);
+            goto out;
+        }
+
+        rc = fork(d, pd);
+
+        if ( rc == -ERESTART )
+            rc = hypercall_create_continuation(__HYPERVISOR_memory_op,
+                                               "lh", XENMEM_sharing_op,
+                                               arg);
+        rcu_unlock_domain(pd);
+        break;
+    }
+
     default:
         rc = -ENOSYS;
         break;
diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
index d93c418bcf..0d0e34e81e 100644
--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -509,6 +509,12 @@ mfn_t __get_gfn_type_access(struct p2m_domain *p2m, unsigned long gfn_l,
 
     mfn = p2m->get_entry(p2m, gfn, t, a, q, page_order, NULL);
 
+    /* Check if we need to fork the page */
+    if ( (q & P2M_ALLOC) && p2m_is_hole(*t) &&
+         !mem_sharing_fork_page(p2m->domain, gfn, q & P2M_UNSHARE) )
+        mfn = p2m->get_entry(p2m, gfn, t, a, q, page_order, NULL);
+
+    /* Check if we need to unshare the page */
     if ( (q & P2M_UNSHARE) && p2m_is_shared(*t) )
     {
         ASSERT(p2m_is_hostp2m(p2m));
@@ -588,7 +594,8 @@ struct page_info *p2m_get_page_from_gfn(
             return page;
 
         /* Error path: not a suitable GFN at all */
-        if ( !p2m_is_ram(*t) && !p2m_is_paging(*t) && !p2m_is_pod(*t) )
+        if ( !p2m_is_ram(*t) && !p2m_is_paging(*t) && !p2m_is_pod(*t) &&
+             !mem_sharing_is_fork(p2m->domain) )
             return NULL;
     }
 
diff --git a/xen/include/asm-arm/page.h b/xen/include/asm-arm/page.h
index 37e1d9aadb..4ea8e97247 100644
--- a/xen/include/asm-arm/page.h
+++ b/xen/include/asm-arm/page.h
@@ -12,6 +12,7 @@
 #define PADDR_BITS              40
 #endif
 #define PADDR_MASK              ((1ULL << PADDR_BITS)-1)
+#define PAGE_OFFSET(ptr)        ((vaddr_t)(ptr) & ~PAGE_MASK)
 
 #define VADDR_BITS              32
 #define VADDR_MASK              (~0UL)
diff --git a/xen/include/asm-x86/hap.h b/xen/include/asm-x86/hap.h
index b94bfb4ed0..1bf07e49fe 100644
--- a/xen/include/asm-x86/hap.h
+++ b/xen/include/asm-x86/hap.h
@@ -45,6 +45,7 @@ int   hap_track_dirty_vram(struct domain *d,
 
 extern const struct paging_mode *hap_paging_get_mode(struct vcpu *);
 int hap_set_allocation(struct domain *d, unsigned int pages, bool *preempted);
+unsigned int hap_get_allocation(struct domain *d);
 
 #endif /* XEN_HAP_H */
 
diff --git a/xen/include/asm-x86/hvm/hvm.h b/xen/include/asm-x86/hvm/hvm.h
index b007b2e343..f283c7d187 100644
--- a/xen/include/asm-x86/hvm/hvm.h
+++ b/xen/include/asm-x86/hvm/hvm.h
@@ -336,6 +336,8 @@ unsigned long hvm_cr4_guest_valid_bits(const struct domain *d, bool restore);
 
 int hvm_copy_context_and_params(struct domain *src, struct domain *dst);
 
+int hvm_get_param(struct domain *d, uint32_t index, uint64_t *value);
+
 #ifdef CONFIG_HVM
 
 #define hvm_get_guest_tsc(v) hvm_get_guest_tsc_fixed(v, 0)
diff --git a/xen/include/asm-x86/mem_sharing.h b/xen/include/asm-x86/mem_sharing.h
index 53b7929d0e..cf7a12f4d2 100644
--- a/xen/include/asm-x86/mem_sharing.h
+++ b/xen/include/asm-x86/mem_sharing.h
@@ -77,6 +77,14 @@ static inline int mem_sharing_unshare_page(struct domain *d,
     return rc;
 }
 
+static inline bool mem_sharing_is_fork(const struct domain *d)
+{
+    return d->parent;
+}
+
+int mem_sharing_fork_page(struct domain *d, gfn_t gfn,
+                          bool unsharing);
+
 /*
  * If called by a foreign domain, possible errors are
  *   -EBUSY -> ring full
@@ -130,6 +138,16 @@ static inline int mem_sharing_notify_enomem(struct domain *d, unsigned long gfn,
     return -EOPNOTSUPP;
 }
 
+static inline bool mem_sharing_is_fork(const struct domain *d)
+{
+    return false;
+}
+
+static inline int mem_sharing_fork_page(struct domain *d, gfn_t gfn, bool lock)
+{
+    return -EOPNOTSUPP;
+}
+
 #endif
 
 #endif /* __MEM_SHARING_H__ */
diff --git a/xen/include/asm-x86/page.h b/xen/include/asm-x86/page.h
index c98d8f5ede..eb73a0fc23 100644
--- a/xen/include/asm-x86/page.h
+++ b/xen/include/asm-x86/page.h
@@ -10,6 +10,7 @@
 #define PAGE_SIZE           (_AC(1,L) << PAGE_SHIFT)
 #define PAGE_MASK           (~(PAGE_SIZE-1))
 #define PAGE_FLAG_MASK      (~0)
+#define PAGE_OFFSET(ptr)    ((unsigned long)(ptr) & ~PAGE_MASK)
 
 #define PAGE_ORDER_4K       0
 #define PAGE_ORDER_2M       9
diff --git a/xen/include/public/memory.h b/xen/include/public/memory.h
index 126d0ff06e..5ee4e0da12 100644
--- a/xen/include/public/memory.h
+++ b/xen/include/public/memory.h
@@ -482,6 +482,7 @@ DEFINE_XEN_GUEST_HANDLE(xen_mem_access_op_t);
 #define XENMEM_sharing_op_add_physmap       6
 #define XENMEM_sharing_op_audit             7
 #define XENMEM_sharing_op_range_share       8
+#define XENMEM_sharing_op_fork              9
 
 #define XENMEM_SHARING_OP_S_HANDLE_INVALID  (-10)
 #define XENMEM_SHARING_OP_C_HANDLE_INVALID  (-9)
@@ -532,6 +533,10 @@ struct xen_mem_sharing_op {
                 uint32_t gref;     /* IN: gref to debug         */
             } u;
         } debug;
+        struct mem_sharing_op_fork {      /* OP_FORK */
+            domid_t parent_domain;        /* IN: parent's domain id */
+            uint16_t pad[3];              /* Must be set to 0 */
+        } fork;
     } u;
 };
 typedef struct xen_mem_sharing_op xen_mem_sharing_op_t;
diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
index 4b78291d51..195e7ee583 100644
--- a/xen/include/xen/sched.h
+++ b/xen/include/xen/sched.h
@@ -481,6 +481,7 @@ struct domain
     /* Memory sharing support */
 #ifdef CONFIG_MEM_SHARING
     struct vm_event_domain *vm_event_share;
+    struct domain *parent; /* VM fork parent */
 #endif
     /* Memory paging support */
 #ifdef CONFIG_HAS_MEM_PAGING
