diff --git a/docs/man/xl.cfg.5.pod.in b/docs/man/xl.cfg.5.pod.in
index ad81af1ed8..355c654693 100644
--- a/docs/man/xl.cfg.5.pod.in
+++ b/docs/man/xl.cfg.5.pod.in
@@ -2167,11 +2167,19 @@ This group incorporates the crash control MSRs. These enlightenments
 allow Windows to write crash information such that it can be logged
 by Xen.
 
+=item B<stimer>
+
+This set incorporates the SynIC and synthetic timer MSRs. Windows will
+use synthetic timers in preference to emulated HPET for a source of
+ticks and hence enabling this group will ensure that ticks will be
+consistent with use of an enlightened time source (B<time_ref_count> or
+B<reference_tsc>).
+
 =item B<defaults>
 
 This is a special value that enables the default set of groups, which
-is currently the B<base>, B<freq>, B<time_ref_count>, B<apic_assist>
-and B<crash_ctl> groups.
+is currently the B<base>, B<freq>, B<time_ref_count>, B<apic_assist>,
+B<crash_ctl> and B<stimer> groups.
 
 =item B<all>
 
diff --git a/tools/libxl/libxl.h b/tools/libxl/libxl.h
index a923a380d3..c8f219b0d3 100644
--- a/tools/libxl/libxl.h
+++ b/tools/libxl/libxl.h
@@ -324,6 +324,12 @@
  */
 #define LIBXL_HAVE_VIRIDIAN_SYNIC 1
 
+/*
+ * LIBXL_HAVE_VIRIDIAN_STIMER indicates that the 'stimer' value
+ * is present in the viridian enlightenment enumeration.
+ */
+#define LIBXL_HAVE_VIRIDIAN_STIMER 1
+
 /*
  * LIBXL_HAVE_BUILDINFO_HVM_ACPI_LAPTOP_SLATE indicates that
  * libxl_domain_build_info has the u.hvm.acpi_laptop_slate field.
diff --git a/tools/libxl/libxl_dom.c b/tools/libxl/libxl_dom.c
index fb758d2ac3..2ee0f82ee7 100644
--- a/tools/libxl/libxl_dom.c
+++ b/tools/libxl/libxl_dom.c
@@ -269,6 +269,7 @@ static int hvm_set_viridian_features(libxl__gc *gc, uint32_t domid,
         libxl_bitmap_set(&enlightenments, LIBXL_VIRIDIAN_ENLIGHTENMENT_TIME_REF_COUNT);
         libxl_bitmap_set(&enlightenments, LIBXL_VIRIDIAN_ENLIGHTENMENT_APIC_ASSIST);
         libxl_bitmap_set(&enlightenments, LIBXL_VIRIDIAN_ENLIGHTENMENT_CRASH_CTL);
+        libxl_bitmap_set(&enlightenments, LIBXL_VIRIDIAN_ENLIGHTENMENT_STIMER);
     }
 
     libxl_for_each_set_bit(v, info->u.hvm.viridian_enable) {
@@ -320,6 +321,9 @@ static int hvm_set_viridian_features(libxl__gc *gc, uint32_t domid,
     if (libxl_bitmap_test(&enlightenments, LIBXL_VIRIDIAN_ENLIGHTENMENT_SYNIC))
         mask |= HVMPV_synic;
 
+    if (libxl_bitmap_test(&enlightenments, LIBXL_VIRIDIAN_ENLIGHTENMENT_STIMER))
+        mask |= HVMPV_time_ref_count | HVMPV_synic | HVMPV_stimer;
+
     if (mask != 0 &&
         xc_hvm_param_set(CTX->xch,
                          domid,
diff --git a/tools/libxl/libxl_types.idl b/tools/libxl/libxl_types.idl
index 9860bcaf5f..1cce249de4 100644
--- a/tools/libxl/libxl_types.idl
+++ b/tools/libxl/libxl_types.idl
@@ -236,6 +236,7 @@ libxl_viridian_enlightenment = Enumeration("viridian_enlightenment", [
     (5, "apic_assist"),
     (6, "crash_ctl"),
     (7, "synic"),
+    (8, "stimer"),
     ])
 
 libxl_hdtype = Enumeration("hdtype", [
diff --git a/xen/arch/x86/hvm/viridian/private.h b/xen/arch/x86/hvm/viridian/private.h
index 96a784b840..c272c34cda 100644
--- a/xen/arch/x86/hvm/viridian/private.h
+++ b/xen/arch/x86/hvm/viridian/private.h
@@ -74,6 +74,11 @@
 int viridian_synic_wrmsr(struct vcpu *v, uint32_t idx, uint64_t val);
 int viridian_synic_rdmsr(const struct vcpu *v, uint32_t idx, uint64_t *val);
 
+bool viridian_synic_deliver_timer_msg(struct vcpu *v, unsigned int sintx,
+                                      unsigned int index,
+                                      uint64_t expiration,
+                                      uint64_t delivery);
+
 int viridian_synic_vcpu_init(const struct vcpu *v);
 int viridian_synic_domain_init(const struct domain *d);
 
@@ -93,7 +98,9 @@ void viridian_synic_load_domain_ctxt(
 int viridian_time_wrmsr(struct vcpu *v, uint32_t idx, uint64_t val);
 int viridian_time_rdmsr(const struct vcpu *v, uint32_t idx, uint64_t *val);
 
-int viridian_time_vcpu_init(const struct vcpu *v);
+void viridian_time_poll_timers(struct vcpu *v);
+
+int viridian_time_vcpu_init(struct vcpu *v);
 int viridian_time_domain_init(const struct domain *d);
 
 void viridian_time_vcpu_deinit(const struct vcpu *v);
diff --git a/xen/arch/x86/hvm/viridian/synic.c b/xen/arch/x86/hvm/viridian/synic.c
index 84ab02694f..2791021bcc 100644
--- a/xen/arch/x86/hvm/viridian/synic.c
+++ b/xen/arch/x86/hvm/viridian/synic.c
@@ -346,9 +346,60 @@ void viridian_synic_domain_deinit(const struct domain *d)
 {
 }
 
-void viridian_synic_poll(const struct vcpu *v)
+void viridian_synic_poll(struct vcpu *v)
 {
-    /* There are currently no message sources */
+    viridian_time_poll_timers(v);
+}
+
+bool viridian_synic_deliver_timer_msg(struct vcpu *v, unsigned int sintx,
+                                      unsigned int index,
+                                      uint64_t expiration,
+                                      uint64_t delivery)
+{
+    struct viridian_vcpu *vv = v->arch.hvm.viridian;
+    const union viridian_sint_msr *vs = &vv->sint[sintx];
+    HV_MESSAGE *msg = vv->simp.ptr;
+    struct {
+        uint32_t TimerIndex;
+        uint32_t Reserved;
+        uint64_t ExpirationTime;
+        uint64_t DeliveryTime;
+    } payload = {
+        .TimerIndex = index,
+        .ExpirationTime = expiration,
+        .DeliveryTime = delivery,
+    };
+
+    if ( test_bit(sintx, &vv->msg_pending) )
+        return false;
+
+    /*
+     * To avoid using an atomic test-and-set, and barrier before calling
+     * vlapic_set_irq(), this function must be called in context of the
+     * vcpu receiving the message.
+     */
+    ASSERT(v == current);
+
+    msg += sintx;
+
+    if ( msg->Header.MessageType != HvMessageTypeNone )
+    {
+        msg->Header.MessageFlags.MessagePending = 1;
+        __set_bit(sintx, &vv->msg_pending);
+        return false;
+    }
+
+    msg->Header.MessageType = HvMessageTimerExpired;
+    msg->Header.MessageFlags.MessagePending = 0;
+    msg->Header.PayloadSize = sizeof(payload);
+
+    BUILD_BUG_ON(sizeof(payload) > sizeof(msg->Payload));
+    memcpy(msg->Payload, &payload, sizeof(payload));
+
+    if ( !vs->mask )
+        vlapic_set_irq(vcpu_vlapic(v), vs->vector, 0);
+
+    return true;
 }
 
 bool viridian_synic_is_auto_eoi_sint(const struct vcpu *v,
diff --git a/xen/arch/x86/hvm/viridian/time.c b/xen/arch/x86/hvm/viridian/time.c
index 71291d921c..8e9dac5a5a 100644
--- a/xen/arch/x86/hvm/viridian/time.c
+++ b/xen/arch/x86/hvm/viridian/time.c
@@ -12,6 +12,7 @@
 #include <xen/version.h>
 
 #include <asm/apic.h>
+#include <asm/event.h>
 #include <asm/hvm/support.h>
 
 #include "private.h"
@@ -27,8 +28,10 @@ typedef struct _HV_REFERENCE_TSC_PAGE
 
 static void update_reference_tsc(struct domain *d, bool initialize)
 {
-    const struct viridian_page *rt = &d->arch.hvm.viridian->reference_tsc;
+    struct viridian_domain *vd = d->arch.hvm.viridian;
+    const struct viridian_page *rt = &vd->reference_tsc;
     HV_REFERENCE_TSC_PAGE *p = rt->ptr;
+    uint32_t seq;
 
     if ( initialize )
         clear_page(p);
@@ -59,6 +62,8 @@ static void update_reference_tsc(struct domain *d, bool initialize)
 
         printk(XENLOG_G_INFO "d%d: VIRIDIAN REFERENCE_TSC: invalidated\n",
                d->domain_id);
+
+        vd->reference_tsc_valid = false;
         return;
     }
 
@@ -72,11 +77,14 @@ static void update_reference_tsc(struct domain *d, bool initialize)
      * ticks per 100ns shifted left by 64.
      */
     p->TscScale = ((10000ul << 32) / d->arch.tsc_khz) << 32;
+    smp_wmb();
+
+    seq = p->TscSequence + 1;
+    if ( seq == 0xFFFFFFFF || seq == 0 ) /* Avoid both 'invalid' values */
+        seq = 1;
 
-    p->TscSequence++;
-    if ( p->TscSequence == 0xFFFFFFFF ||
-         p->TscSequence == 0 ) /* Avoid both 'invalid' values */
-        p->TscSequence = 1;
+    p->TscSequence = seq;
+    vd->reference_tsc_valid = true;
 }
 
 static int64_t raw_trc_val(const struct domain *d)
@@ -118,18 +126,253 @@ static int64_t time_ref_count(const struct domain *d)
     return raw_trc_val(d) + trc->off;
 }
 
+/*
+ * The specification says: "The partition reference time is computed
+ * by the following formula:
+ *
+ * ReferenceTime = ((VirtualTsc * TscScale) >> 64) + TscOffset
+ *
+ * The multiplication is a 64 bit multiplication, which results in a
+ * 128 bit number which is then shifted 64 times to the right to obtain
+ * the high 64 bits."
+ */
+static uint64_t scale_tsc(uint64_t tsc, uint64_t scale, uint64_t offset)
+{
+    uint64_t result;
+
+    /*
+     * Quadword MUL takes an implicit operand in RAX, and puts the result
+     * in RDX:RAX. Because we only want the result of the multiplication
+     * after shifting right by 64 bits, we therefore only need the content
+     * of RDX.
+     */
+    asm ( "mulq %[scale]"
+          : "+a" (tsc), "=d" (result)
+          : [scale] "rm" (scale) );
+
+    return result + offset;
+}
+
+static uint64_t time_now(struct domain *d)
+{
+    uint64_t tsc, scale;
+
+    /*
+     * If the reference TSC page is not enabled, or has been invalidated
+     * fall back to the partition reference counter.
+     */
+    if ( !d->arch.hvm.viridian->reference_tsc_valid )
+        return time_ref_count(d);
+
+    /* Otherwise compute reference time in the same way the guest would */
+    tsc = hvm_get_guest_tsc(pt_global_vcpu_target(d));
+    scale = ((10000ul << 32) / d->arch.tsc_khz) << 32;
+
+    return scale_tsc(tsc, scale, 0);
+}
+
+static void stop_stimer(struct viridian_stimer *vs)
+{
+    if ( !vs->started )
+        return;
+
+    stop_timer(&vs->timer);
+    vs->started = false;
+}
+
+static void stimer_expire(void *data)
+{
+    struct viridian_stimer *vs = data;
+    struct vcpu *v = vs->v;
+    struct viridian_vcpu *vv = v->arch.hvm.viridian;
+    unsigned int stimerx = vs - &vv->stimer[0];
+
+    set_bit(stimerx, &vv->stimer_pending);
+    vcpu_kick(v);
+}
+
+static void start_stimer(struct viridian_stimer *vs)
+{
+    const struct vcpu *v = vs->v;
+    struct viridian_vcpu *vv = v->arch.hvm.viridian;
+    unsigned int stimerx = vs - &vv->stimer[0];
+    int64_t now = time_now(v->domain);
+    int64_t expiration;
+    s_time_t timeout;
+
+    if ( !test_and_set_bit(stimerx, &vv->stimer_enabled) )
+        printk(XENLOG_G_INFO "%pv: VIRIDIAN STIMER%u: enabled\n", v,
+               stimerx);
+
+    if ( vs->config.periodic )
+    {
+        /*
+         * The specification says that if the timer is lazy then we
+         * skip over any missed expirations so we can treat this case
+         * as the same as if the timer is currently stopped, i.e. we
+         * just schedule expiration to be 'count' ticks from now.
+         */
+        if ( !vs->started || vs->config.lazy )
+            expiration = now + vs->count;
+        else
+        {
+            unsigned int missed = 0;
+
+            /*
+             * The timer is already started, so we're re-scheduling.
+             * Hence advance the timer expiration by one tick.
+             */
+            expiration = vs->expiration + vs->count;
+
+            /* Now check to see if any expirations have been missed */
+            if ( expiration - now <= 0 )
+                missed = ((now - expiration) / vs->count) + 1;
+
+            /*
+             * The specification says that if the timer is not lazy then
+             * a non-zero missed count should be used to reduce the period
+             * of the timer until it catches up, unless the count has
+             * reached a 'significant number', in which case the timer
+             * should be treated as lazy. Unfortunately the specification
+             * does not state what that number is so the choice of number
+             * here is a pure guess.
+             */
+            if ( missed > 3 )
+                expiration = now + vs->count;
+            else if ( missed )
+                expiration = now + (vs->count / missed);
+        }
+    }
+    else
+    {
+        expiration = vs->count;
+        if ( expiration - now <= 0 )
+        {
+            vs->expiration = expiration;
+            stimer_expire(vs);
+            return;
+        }
+    }
+    ASSERT(expiration - now > 0);
+
+    vs->expiration = expiration;
+    timeout = (expiration - now) * 100ull;
+
+    vs->started = true;
+    clear_bit(stimerx, &vv->stimer_pending);
+    migrate_timer(&vs->timer, v->processor);
+    set_timer(&vs->timer, timeout + NOW());
+}
+
+static void poll_stimer(struct vcpu *v, unsigned int stimerx)
+{
+    struct viridian_vcpu *vv = v->arch.hvm.viridian;
+    struct viridian_stimer *vs = &vv->stimer[stimerx];
+
+    /*
+     * Timer expiry may race with the timer being disabled. If the timer
+     * is disabled make sure the pending bit is cleared to avoid re-
+     * polling.
+     */
+    if ( !vs->config.enabled )
+    {
+        clear_bit(stimerx, &vv->stimer_pending);
+        return;
+    }
+
+    if ( !test_bit(stimerx, &vv->stimer_pending) )
+        return;
+
+    if ( !viridian_synic_deliver_timer_msg(v, vs->config.sintx,
+                                           stimerx, vs->expiration,
+                                           time_now(v->domain)) )
+        return;
+
+    clear_bit(stimerx, &vv->stimer_pending);
+
+    if ( vs->config.periodic )
+        start_stimer(vs);
+    else
+        vs->config.enabled = 0;
+}
+
+void viridian_time_poll_timers(struct vcpu *v)
+{
+    struct viridian_vcpu *vv = v->arch.hvm.viridian;
+    unsigned int i;
+
+    if ( !vv->stimer_pending )
+       return;
+
+    for ( i = 0; i < ARRAY_SIZE(vv->stimer); i++ )
+        poll_stimer(v, i);
+}
+
+void viridian_time_vcpu_freeze(struct vcpu *v)
+{
+    struct viridian_vcpu *vv = v->arch.hvm.viridian;
+    unsigned int i;
+
+    if ( !is_viridian_vcpu(v) ||
+         !(viridian_feature_mask(v->domain) & HVMPV_stimer) )
+        return;
+
+    for ( i = 0; i < ARRAY_SIZE(vv->stimer); i++ )
+    {
+        struct viridian_stimer *vs = &vv->stimer[i];
+
+        if ( vs->started )
+            stop_timer(&vs->timer);
+    }
+}
+
+void viridian_time_vcpu_thaw(struct vcpu *v)
+{
+    struct viridian_vcpu *vv = v->arch.hvm.viridian;
+    unsigned int i;
+
+    if ( !is_viridian_vcpu(v) ||
+         !(viridian_feature_mask(v->domain) & HVMPV_stimer) )
+        return;
+
+    for ( i = 0; i < ARRAY_SIZE(vv->stimer); i++ )
+    {
+        struct viridian_stimer *vs = &vv->stimer[i];
+
+        if ( vs->config.enabled )
+            start_stimer(vs);
+    }
+}
+
 void viridian_time_domain_freeze(const struct domain *d)
 {
+    struct vcpu *v;
+
+    if ( !is_viridian_domain(d) )
+        return;
+
+    for_each_vcpu ( d, v )
+        viridian_time_vcpu_freeze(v);
+
     time_ref_count_freeze(d);
 }
 
 void viridian_time_domain_thaw(const struct domain *d)
 {
+    struct vcpu *v;
+
+    if ( !is_viridian_domain(d) )
+        return;
+
     time_ref_count_thaw(d);
+
+    for_each_vcpu ( d, v )
+        viridian_time_vcpu_thaw(v);
 }
 
 int viridian_time_wrmsr(struct vcpu *v, uint32_t idx, uint64_t val)
 {
+    struct viridian_vcpu *vv = v->arch.hvm.viridian;
     struct domain *d = v->domain;
     struct viridian_domain *vd = d->arch.hvm.viridian;
 
@@ -149,6 +392,61 @@ int viridian_time_wrmsr(struct vcpu *v, uint32_t idx, uint64_t val)
         }
         break;
 
+    case HV_X64_MSR_TIME_REF_COUNT:
+        return X86EMUL_EXCEPTION;
+
+    case HV_X64_MSR_STIMER0_CONFIG:
+    case HV_X64_MSR_STIMER1_CONFIG:
+    case HV_X64_MSR_STIMER2_CONFIG:
+    case HV_X64_MSR_STIMER3_CONFIG:
+    {
+        unsigned int stimerx = (idx - HV_X64_MSR_STIMER0_CONFIG) / 2;
+        struct viridian_stimer *vs =
+            &array_access_nospec(vv->stimer, stimerx);
+
+        if ( !(viridian_feature_mask(d) & HVMPV_stimer) )
+            return X86EMUL_EXCEPTION;
+
+        stop_stimer(vs);
+
+        vs->config.raw = val;
+
+        if ( !vs->config.sintx )
+            vs->config.enabled = 0;
+
+        if ( vs->config.enabled )
+            start_stimer(vs);
+
+        break;
+    }
+
+    case HV_X64_MSR_STIMER0_COUNT:
+    case HV_X64_MSR_STIMER1_COUNT:
+    case HV_X64_MSR_STIMER2_COUNT:
+    case HV_X64_MSR_STIMER3_COUNT:
+    {
+        unsigned int stimerx = (idx - HV_X64_MSR_STIMER0_CONFIG) / 2;
+        struct viridian_stimer *vs =
+            &array_access_nospec(vv->stimer, stimerx);
+
+        if ( !(viridian_feature_mask(d) & HVMPV_stimer) )
+            return X86EMUL_EXCEPTION;
+
+        stop_stimer(vs);
+
+        vs->count = val;
+
+        if ( !vs->count  )
+            vs->config.enabled = 0;
+        else if ( vs->config.auto_enable )
+            vs->config.enabled = 1;
+
+        if ( vs->config.enabled )
+            start_stimer(vs);
+
+        break;
+    }
+
     default:
         gdprintk(XENLOG_INFO, "%s: unimplemented MSR %#x (%016"PRIx64")\n",
                  __func__, idx, val);
@@ -160,6 +458,7 @@ int viridian_time_wrmsr(struct vcpu *v, uint32_t idx, uint64_t val)
 
 int viridian_time_rdmsr(const struct vcpu *v, uint32_t idx, uint64_t *val)
 {
+    const struct viridian_vcpu *vv = v->arch.hvm.viridian;
     const struct domain *d = v->domain;
     struct viridian_domain *vd = d->arch.hvm.viridian;
 
@@ -201,6 +500,38 @@ int viridian_time_rdmsr(const struct vcpu *v, uint32_t idx, uint64_t *val)
         break;
     }
 
+    case HV_X64_MSR_STIMER0_CONFIG:
+    case HV_X64_MSR_STIMER1_CONFIG:
+    case HV_X64_MSR_STIMER2_CONFIG:
+    case HV_X64_MSR_STIMER3_CONFIG:
+    {
+        unsigned int stimerx = (idx - HV_X64_MSR_STIMER0_CONFIG) / 2;
+        const struct viridian_stimer *vs =
+            &array_access_nospec(vv->stimer, stimerx);
+
+        if ( !(viridian_feature_mask(d) & HVMPV_stimer) )
+            return X86EMUL_EXCEPTION;
+
+        *val = vs->config.raw;
+        break;
+    }
+
+    case HV_X64_MSR_STIMER0_COUNT:
+    case HV_X64_MSR_STIMER1_COUNT:
+    case HV_X64_MSR_STIMER2_COUNT:
+    case HV_X64_MSR_STIMER3_COUNT:
+    {
+        unsigned int stimerx = (idx - HV_X64_MSR_STIMER0_CONFIG) / 2;
+        const struct viridian_stimer *vs =
+            &array_access_nospec(vv->stimer, stimerx);
+
+        if ( !(viridian_feature_mask(d) & HVMPV_stimer) )
+            return X86EMUL_EXCEPTION;
+
+        *val = vs->count;
+        break;
+    }
+
     default:
         gdprintk(XENLOG_INFO, "%s: unimplemented MSR %#x\n", __func__, idx);
         return X86EMUL_EXCEPTION;
@@ -209,8 +540,19 @@ int viridian_time_rdmsr(const struct vcpu *v, uint32_t idx, uint64_t *val)
     return X86EMUL_OKAY;
 }
 
-int viridian_time_vcpu_init(const struct vcpu *v)
+int viridian_time_vcpu_init(struct vcpu *v)
 {
+    struct viridian_vcpu *vv = v->arch.hvm.viridian;
+    unsigned int i;
+
+    for ( i = 0; i < ARRAY_SIZE(vv->stimer); i++ )
+    {
+        struct viridian_stimer *vs = &vv->stimer[i];
+
+        vs->v = v;
+        init_timer(&vs->timer, stimer_expire, vs, v->processor);
+    }
+
     return 0;
 }
 
@@ -221,6 +563,16 @@ int viridian_time_domain_init(const struct domain *d)
 
 void viridian_time_vcpu_deinit(const struct vcpu *v)
 {
+    struct viridian_vcpu *vv = v->arch.hvm.viridian;
+    unsigned int i;
+
+    for ( i = 0; i < ARRAY_SIZE(vv->stimer); i++ )
+    {
+        struct viridian_stimer *vs = &vv->stimer[i];
+
+        kill_timer(&vs->timer);
+        vs->v = NULL;
+    }
 }
 
 void viridian_time_domain_deinit(const struct domain *d)
@@ -231,11 +583,36 @@ void viridian_time_domain_deinit(const struct domain *d)
 void viridian_time_save_vcpu_ctxt(
     const struct vcpu *v, struct hvm_viridian_vcpu_context *ctxt)
 {
+    const struct viridian_vcpu *vv = v->arch.hvm.viridian;
+    unsigned int i;
+
+    BUILD_BUG_ON(ARRAY_SIZE(vv->stimer) !=
+                 ARRAY_SIZE(ctxt->stimer_config_msr));
+    BUILD_BUG_ON(ARRAY_SIZE(vv->stimer) !=
+                 ARRAY_SIZE(ctxt->stimer_count_msr));
+
+    for ( i = 0; i < ARRAY_SIZE(vv->stimer); i++ )
+    {
+        const struct viridian_stimer *vs = &vv->stimer[i];
+
+        ctxt->stimer_config_msr[i] = vs->config.raw;
+        ctxt->stimer_count_msr[i] = vs->count;
+    }
 }
 
 void viridian_time_load_vcpu_ctxt(
     struct vcpu *v, const struct hvm_viridian_vcpu_context *ctxt)
 {
+    struct viridian_vcpu *vv = v->arch.hvm.viridian;
+    unsigned int i;
+
+    for ( i = 0; i < ARRAY_SIZE(vv->stimer); i++ )
+    {
+        struct viridian_stimer *vs = &vv->stimer[i];
+
+        vs->config.raw = ctxt->stimer_config_msr[i];
+        vs->count = ctxt->stimer_count_msr[i];
+    }
 }
 
 void viridian_time_save_domain_ctxt(
diff --git a/xen/arch/x86/hvm/viridian/viridian.c b/xen/arch/x86/hvm/viridian/viridian.c
index f3166fbcd0..dce648bb4e 100644
--- a/xen/arch/x86/hvm/viridian/viridian.c
+++ b/xen/arch/x86/hvm/viridian/viridian.c
@@ -181,6 +181,8 @@ void cpuid_viridian_leaves(const struct vcpu *v, uint32_t leaf,
             mask.AccessPartitionReferenceTsc = 1;
         if ( viridian_feature_mask(d) & HVMPV_synic )
             mask.AccessSynicRegs = 1;
+        if ( viridian_feature_mask(d) & HVMPV_stimer )
+            mask.AccessSyntheticTimerRegs = 1;
 
         u.mask = mask;
 
@@ -322,6 +324,8 @@ int guest_wrmsr_viridian(struct vcpu *v, uint32_t idx, uint64_t val)
     case HV_X64_MSR_TSC_FREQUENCY:
     case HV_X64_MSR_APIC_FREQUENCY:
     case HV_X64_MSR_REFERENCE_TSC:
+    case HV_X64_MSR_TIME_REF_COUNT:
+    case HV_X64_MSR_STIMER0_CONFIG ... HV_X64_MSR_STIMER3_COUNT:
         return viridian_time_wrmsr(v, idx, val);
 
     case HV_X64_MSR_CRASH_P0:
@@ -403,6 +407,7 @@ int guest_rdmsr_viridian(const struct vcpu *v, uint32_t idx, uint64_t *val)
     case HV_X64_MSR_APIC_FREQUENCY:
     case HV_X64_MSR_REFERENCE_TSC:
     case HV_X64_MSR_TIME_REF_COUNT:
+    case HV_X64_MSR_STIMER0_CONFIG ... HV_X64_MSR_STIMER3_COUNT:
         return viridian_time_rdmsr(v, idx, val);
 
     case HV_X64_MSR_CRASH_P0:
diff --git a/xen/include/asm-x86/hvm/viridian.h b/xen/include/asm-x86/hvm/viridian.h
index 03fc4c6b76..54e46cc4c4 100644
--- a/xen/include/asm-x86/hvm/viridian.h
+++ b/xen/include/asm-x86/hvm/viridian.h
@@ -40,6 +40,32 @@ union viridian_sint_msr
     };
 };
 
+union viridian_stimer_config_msr
+{
+    uint64_t raw;
+    struct
+    {
+        uint64_t enabled:1;
+        uint64_t periodic:1;
+        uint64_t lazy:1;
+        uint64_t auto_enable:1;
+        uint64_t vector:8;
+        uint64_t direct_mode:1;
+        uint64_t reserved_zero1:3;
+        uint64_t sintx:4;
+        uint64_t reserved_zero2:44;
+    };
+};
+
+struct viridian_stimer {
+    struct vcpu *v;
+    struct timer timer;
+    union viridian_stimer_config_msr config;
+    uint64_t count;
+    uint64_t expiration;
+    bool started;
+};
+
 struct viridian_vcpu
 {
     struct viridian_page vp_assist;
@@ -51,6 +77,9 @@ struct viridian_vcpu
     struct viridian_page simp;
     union viridian_sint_msr sint[16];
     uint8_t vector_to_sintx[256];
+    struct viridian_stimer stimer[4];
+    unsigned int stimer_enabled;
+    unsigned int stimer_pending;
     uint64_t crash_param[5];
 };
 
@@ -87,6 +116,7 @@ struct viridian_domain
     union viridian_page_msr hypercall_gpa;
     struct viridian_time_ref_count time_ref_count;
     struct viridian_page reference_tsc;
+    bool reference_tsc_valid;
 };
 
 void cpuid_viridian_leaves(const struct vcpu *v, uint32_t leaf,
@@ -111,7 +141,7 @@ void viridian_apic_assist_set(const struct vcpu *v);
 bool viridian_apic_assist_completed(const struct vcpu *v);
 void viridian_apic_assist_clear(const struct vcpu *v);
 
-void viridian_synic_poll(const struct vcpu *v);
+void viridian_synic_poll(struct vcpu *v);
 bool viridian_synic_is_auto_eoi_sint(const struct vcpu *v,
                                      unsigned int vector);
 void viridian_synic_ack_sint(const struct vcpu *v, unsigned int vector);
diff --git a/xen/include/public/arch-x86/hvm/save.h b/xen/include/public/arch-x86/hvm/save.h
index ec3e4df12c..8344aa471f 100644
--- a/xen/include/public/arch-x86/hvm/save.h
+++ b/xen/include/public/arch-x86/hvm/save.h
@@ -604,6 +604,8 @@ struct hvm_viridian_vcpu_context {
     uint8_t  _pad[7];
     uint64_t simp_msr;
     uint64_t sint_msr[16];
+    uint64_t stimer_config_msr[4];
+    uint64_t stimer_count_msr[4];
 };
 
 DECLARE_HVM_SAVE_TYPE(VIRIDIAN_VCPU, 17, struct hvm_viridian_vcpu_context);
diff --git a/xen/include/public/hvm/params.h b/xen/include/public/hvm/params.h
index e7e3c7c892..e06b0942d0 100644
--- a/xen/include/public/hvm/params.h
+++ b/xen/include/public/hvm/params.h
@@ -150,6 +150,10 @@
 #define _HVMPV_synic 7
 #define HVMPV_synic (1 << _HVMPV_synic)
 
+/* Enable STIMER MSRs */
+#define _HVMPV_stimer 8
+#define HVMPV_stimer (1 << _HVMPV_stimer)
+
 #define HVMPV_feature_mask \
         (HVMPV_base_freq | \
          HVMPV_no_freq | \
@@ -158,7 +162,8 @@
          HVMPV_hcall_remote_tlb_flush | \
          HVMPV_apic_assist | \
          HVMPV_crash_ctl | \
-         HVMPV_synic)
+         HVMPV_synic | \
+         HVMPV_stimer)
 
 #endif
 
