diff --git a/hw/i386/kvm/xen_evtchn.c b/hw/i386/kvm/xen_evtchn.c
index 6b0bdba65d..f39b751ff9 100644
--- a/hw/i386/kvm/xen_evtchn.c
+++ b/hw/i386/kvm/xen_evtchn.c
@@ -28,6 +28,8 @@
 #include "hw/sysbus.h"
 #include "hw/xen/xen.h"
 #include "hw/i386/x86.h"
+#include "hw/i386/pc.h"
+#include "hw/pci/pci.h"
 #include "hw/irq.h"
 
 #include "xen_evtchn.h"
@@ -101,6 +103,7 @@ struct XenEvtchnState {
 
     uint64_t callback_param;
     bool evtchn_in_kernel;
+    uint32_t callback_gsi;
 
     QEMUBH *gsi_bh;
 
@@ -217,11 +220,41 @@ static void xen_evtchn_register_types(void)
 
 type_init(xen_evtchn_register_types)
 
+static int set_callback_pci_intx(XenEvtchnState *s, uint64_t param)
+{
+    PCMachineState *pcms = PC_MACHINE(qdev_get_machine());
+    uint8_t pin = param & 3;
+    uint8_t devfn = (param >> 8) & 0xff;
+    uint16_t bus = (param >> 16) & 0xffff;
+    uint16_t domain = (param >> 32) & 0xffff;
+    PCIDevice *pdev;
+    PCIINTxRoute r;
+
+    if (domain || !pcms) {
+        return 0;
+    }
+
+    pdev = pci_find_device(pcms->bus, bus, devfn);
+    if (!pdev) {
+        return 0;
+    }
+
+    r = pci_device_route_intx_to_irq(pdev, pin);
+    if (r.mode != PCI_INTX_ENABLED) {
+        return 0;
+    }
+
+    /*
+     * Hm, can we be notified of INTX routing changes? Not without
+     * *owning* the device and being allowed to overwrite its own
+     * ->intx_routing_notifier, AFAICT. So let's not.
+     */
+    return r.irq;
+}
+
 void xen_evtchn_set_callback_level(int level)
 {
     XenEvtchnState *s = xen_evtchn_singleton;
-    uint32_t param;
-
     if (!s) {
         return;
     }
@@ -260,18 +293,12 @@ void xen_evtchn_set_callback_level(int level)
         return;
     }
 
-    param = (uint32_t)s->callback_param;
-
-    switch (s->callback_param >> CALLBACK_VIA_TYPE_SHIFT) {
-    case HVM_PARAM_CALLBACK_TYPE_GSI:
-        if (param < IOAPIC_NUM_PINS) {
-            qemu_set_irq(s->gsis[param], level);
-            if (level) {
-                /* Ensure the vCPU polls for deassertion */
-                kvm_xen_set_callback_asserted();
-            }
+    if (s->callback_gsi && s->callback_gsi < IOAPIC_NUM_PINS) {
+        qemu_set_irq(s->gsis[s->callback_gsi], level);
+        if (level) {
+            /* Ensure the vCPU polls for deassertion */
+            kvm_xen_set_callback_asserted();
         }
-        break;
     }
 }
 
@@ -283,15 +310,22 @@ int xen_evtchn_set_callback_param(uint64_t param)
         .u.vector = 0,
     };
     bool in_kernel = false;
+    uint32_t gsi = 0;
+    int type = param >> CALLBACK_VIA_TYPE_SHIFT;
     int ret;
 
     if (!s) {
         return -ENOTSUP;
     }
 
+    /*
+     * We need the BQL because set_callback_pci_intx() may call into PCI code,
+     * and because we may need to manipulate the old and new GSI levels.
+     */
+    assert(qemu_mutex_iothread_locked());
     qemu_mutex_lock(&s->port_lock);
 
-    switch (param >> CALLBACK_VIA_TYPE_SHIFT) {
+    switch (type) {
     case HVM_PARAM_CALLBACK_TYPE_VECTOR: {
         xa.u.vector = (uint8_t)param,
 
@@ -299,10 +333,17 @@ int xen_evtchn_set_callback_param(uint64_t param)
         if (!ret && kvm_xen_has_cap(EVTCHN_SEND)) {
             in_kernel = true;
         }
+        gsi = 0;
         break;
     }
 
+    case HVM_PARAM_CALLBACK_TYPE_PCI_INTX:
+        gsi = set_callback_pci_intx(s, param);
+        ret = gsi ? 0 : -EINVAL;
+        break;
+
     case HVM_PARAM_CALLBACK_TYPE_GSI:
+        gsi = (uint32_t)param;
         ret = 0;
         break;
 
@@ -320,6 +361,17 @@ int xen_evtchn_set_callback_param(uint64_t param)
         }
         s->callback_param = param;
         s->evtchn_in_kernel = in_kernel;
+
+        if (gsi != s->callback_gsi) {
+            struct vcpu_info *vi = kvm_xen_get_vcpu_info_hva(0);
+
+            xen_evtchn_set_callback_level(0);
+            s->callback_gsi = gsi;
+
+            if (gsi && vi && vi->evtchn_upcall_pending) {
+                kvm_xen_inject_vcpu_callback_vector(0, type);
+            }
+        }
     }
 
     qemu_mutex_unlock(&s->port_lock);
diff --git a/target/i386/kvm/xen-emu.c b/target/i386/kvm/xen-emu.c
index b52617df54..9e22c9fa02 100644
--- a/target/i386/kvm/xen-emu.c
+++ b/target/i386/kvm/xen-emu.c
@@ -131,6 +131,38 @@ int kvm_xen_init(KVMState *s, uint32_t hypercall_msr)
         return ret;
     }
 
+    /* If called a second time, don't repeat the rest of the setup. */
+    if (s->xen_caps) {
+        return 0;
+    }
+
+    /*
+     * Event channel delivery via GSI/PCI_INTX needs to poll the vcpu_info
+     * of vCPU0 to deassert the IRQ when ->evtchn_upcall_pending is cleared.
+     *
+     * In the kernel, there's a notifier hook on the PIC/IOAPIC which allows
+     * such things to be polled at precisely the right time. We *could* do
+     * it nicely in the kernel: check vcpu_info[0]->evtchn_upcall_pending at
+     * the moment the IRQ is acked, and see if it should be reasserted.
+     *
+     * But the in-kernel irqchip is deprecated, so we're unlikely to add
+     * that support in the kernel. Insist on using the split irqchip mode
+     * instead.
+     *
+     * This leaves us polling for the level going low in QEMU, which lacks
+     * the appropriate hooks in its PIC/IOAPIC code. Even VFIO is sending a
+     * spurious 'ack' to an INTX IRQ every time there's any MMIO access to
+     * the device (for which it has to unmap the device and trap access, for
+     * some period after an IRQ!!). In the Xen case, we do it on exit from
+     * KVM_RUN, if the flag is set to say that the GSI is currently asserted.
+     * Which is kind of icky, but less so than the VFIO one. I may fix them
+     * both later...
+     */
+    if (!kvm_kernel_irqchip_split()) {
+        error_report("kvm: Xen support requires kernel-irqchip=split");
+        return -EINVAL;
+    }
+
     s->xen_caps = xen_caps;
     return 0;
 }
@@ -684,7 +716,9 @@ static bool handle_set_param(struct kvm_xen_exit *exit, X86CPU *cpu,
 
     switch (hp.index) {
     case HVM_PARAM_CALLBACK_IRQ:
+        qemu_mutex_lock_iothread();
         err = xen_evtchn_set_callback_param(hp.value);
+        qemu_mutex_unlock_iothread();
         xen_set_long_mode(exit->u.hcall.longmode);
         break;
     default: