hw/xen: Add xen_gnttab device for grant table emulation

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>

hw/i386/kvm/meson.build

@@ -7,6 +7,7 @@ i386_kvm_ss.add(when: 'CONFIG_IOAPIC', if_true: files('ioapic.c'))
 i386_kvm_ss.add(when: 'CONFIG_XEN_EMU', if_true: files(
   'xen_overlay.c',
   'xen_evtchn.c',
+  'xen_gnttab.c',
   ))
 
 i386_ss.add_all(when: 'CONFIG_KVM', if_true: i386_kvm_ss)

hw/i386/kvm/xen_gnttab.c

@@ -0,0 +1,111 @@
+/*
+ * QEMU Xen emulation: Grant table support
+ *
+ * Copyright © 2022 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ * Authors: David Woodhouse <dwmw2@infradead.org>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+
+#include "qemu/osdep.h"
+#include "qemu/host-utils.h"
+#include "qemu/module.h"
+#include "qemu/lockable.h"
+#include "qemu/main-loop.h"
+#include "qapi/error.h"
+#include "qom/object.h"
+#include "exec/target_page.h"
+#include "exec/address-spaces.h"
+#include "migration/vmstate.h"
+
+#include "hw/sysbus.h"
+#include "hw/xen/xen.h"
+#include "xen_overlay.h"
+#include "xen_gnttab.h"
+
+#include "sysemu/kvm.h"
+#include "sysemu/kvm_xen.h"
+
+#include "hw/xen/interface/memory.h"
+#include "hw/xen/interface/grant_table.h"
+
+#define TYPE_XEN_GNTTAB "xen-gnttab"
+OBJECT_DECLARE_SIMPLE_TYPE(XenGnttabState, XEN_GNTTAB)
+
+#define XEN_PAGE_SHIFT 12
+#define XEN_PAGE_SIZE (1ULL << XEN_PAGE_SHIFT)
+
+struct XenGnttabState {
+    /*< private >*/
+    SysBusDevice busdev;
+    /*< public >*/
+
+    uint32_t nr_frames;
+    uint32_t max_frames;
+};
+
+struct XenGnttabState *xen_gnttab_singleton;
+
+static void xen_gnttab_realize(DeviceState *dev, Error **errp)
+{
+    XenGnttabState *s = XEN_GNTTAB(dev);
+
+    if (xen_mode != XEN_EMULATE) {
+        error_setg(errp, "Xen grant table support is for Xen emulation");
+        return;
+    }
+    s->nr_frames = 0;
+    s->max_frames = kvm_xen_get_gnttab_max_frames();
+}
+
+static bool xen_gnttab_is_needed(void *opaque)
+{
+    return xen_mode == XEN_EMULATE;
+}
+
+static const VMStateDescription xen_gnttab_vmstate = {
+    .name = "xen_gnttab",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .needed = xen_gnttab_is_needed,
+    .fields = (VMStateField[]) {
+        VMSTATE_UINT32(nr_frames, XenGnttabState),
+        VMSTATE_END_OF_LIST()
+    }
+};
+
+static void xen_gnttab_class_init(ObjectClass *klass, void *data)
+{
+    DeviceClass *dc = DEVICE_CLASS(klass);
+
+    dc->realize = xen_gnttab_realize;
+    dc->vmsd = &xen_gnttab_vmstate;
+}
+
+static const TypeInfo xen_gnttab_info = {
+    .name          = TYPE_XEN_GNTTAB,
+    .parent        = TYPE_SYS_BUS_DEVICE,
+    .instance_size = sizeof(XenGnttabState),
+    .class_init    = xen_gnttab_class_init,
+};
+
+void xen_gnttab_create(void)
+{
+    xen_gnttab_singleton = XEN_GNTTAB(sysbus_create_simple(TYPE_XEN_GNTTAB,
+                                                           -1, NULL));
+}
+
+static void xen_gnttab_register_types(void)
+{
+    type_register_static(&xen_gnttab_info);
+}
+
+type_init(xen_gnttab_register_types)
+
+int xen_gnttab_map_page(uint64_t idx, uint64_t gfn)
+{
+    return -ENOSYS;
+}
+

hw/i386/kvm/xen_gnttab.h

@@ -0,0 +1,18 @@
+/*
+ * QEMU Xen emulation: Grant table support
+ *
+ * Copyright © 2022 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ * Authors: David Woodhouse <dwmw2@infradead.org>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+
+#ifndef QEMU_XEN_GNTTAB_H
+#define QEMU_XEN_GNTTAB_H
+
+void xen_gnttab_create(void);
+int xen_gnttab_map_page(uint64_t idx, uint64_t gfn);
+
+#endif /* QEMU_XEN_GNTTAB_H */

hw/i386/pc.c

@@ -92,6 +92,7 @@
 #include "hw/virtio/virtio-mem-pci.h"
 #include "hw/i386/kvm/xen_overlay.h"
 #include "hw/i386/kvm/xen_evtchn.h"
+#include "hw/i386/kvm/xen_gnttab.h"
 #include "hw/mem/memory-device.h"
 #include "sysemu/replay.h"
 #include "target/i386/cpu.h"
@@ -1860,6 +1861,7 @@ int pc_machine_kvm_type(MachineState *machine, const char *kvm_type)
     if (xen_mode == XEN_EMULATE) {
         xen_overlay_create();
         xen_evtchn_create();
+        xen_gnttab_create();
     }
 #endif
     return 0;

target/i386/kvm/xen-emu.c

@@ -25,6 +25,7 @@
 #include "hw/i386/apic-msidef.h"
 #include "hw/i386/kvm/xen_overlay.h"
 #include "hw/i386/kvm/xen_evtchn.h"
+#include "hw/i386/kvm/xen_gnttab.h"
 
 #include "hw/xen/interface/version.h"
 #include "hw/xen/interface/sched.h"
@@ -563,6 +564,8 @@ static int add_to_physmap_one(uint32_t space, uint64_t idx, uint64_t gfn)
         return xen_set_shared_info(gfn);
 
     case XENMAPSPACE_grant_table:
+        return xen_gnttab_map_page(idx, gfn);
+
     case XENMAPSPACE_gmfn:
     case XENMAPSPACE_gmfn_range:
         return -ENOTSUP;