@@ -4,5 +4,6 @@ i386_kvm_ss.add(when: 'CONFIG_APIC', if_true: files('apic.c'))
i386_kvm_ss.add(when: 'CONFIG_I8254', if_true: files('i8254.c'))
i386_kvm_ss.add(when: 'CONFIG_I8259', if_true: files('i8259.c'))
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'))
i386_ss.add_all(when: 'CONFIG_KVM', if_true: i386_kvm_ss)
new file mode 100644
@@ -0,0 +1,205 @@
+/*
+ * QEMU Xen emulation: Shared/overlay pages 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/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 "sysemu/kvm.h"
+#include "sysemu/kvm_xen.h"
+#include <linux/kvm.h>
+
+#include "standard-headers/xen/memory.h"
+
+
+#define TYPE_XEN_OVERLAY "xen-overlay"
+OBJECT_DECLARE_SIMPLE_TYPE(XenOverlayState, XEN_OVERLAY)
+
+#define XEN_PAGE_SHIFT 12
+#define XEN_PAGE_SIZE (1ULL << XEN_PAGE_SHIFT)
+
+struct XenOverlayState {
+ /*< private >*/
+ SysBusDevice busdev;
+ /*< public >*/
+
+ MemoryRegion shinfo_mem;
+ void *shinfo_ptr;
+ uint64_t shinfo_gpa;
+};
+
+struct XenOverlayState *xen_overlay_singleton;
+
+static void xen_overlay_do_map_page(MemoryRegion *page, uint64_t gpa)
+{
+ /*
+ * Xen allows guests to map the same page as many times as it likes
+ * into guest physical frames. We don't, because it would be hard
+ * to track and restore them all. One mapping of each page is
+ * perfectly sufficient for all known guests... and we've tested
+ * that theory on a few now in other implementations. dwmw2.
+ */
+ if (memory_region_is_mapped(page)) {
+ if (gpa == INVALID_GPA) {
+ memory_region_del_subregion(get_system_memory(), page);
+ } else {
+ /* Just move it */
+ memory_region_set_address(page, gpa);
+ }
+ } else if (gpa != INVALID_GPA) {
+ memory_region_add_subregion_overlap(get_system_memory(), gpa, page, 0);
+ }
+}
+
+/* KVM is the only existing back end for now. Let's not overengineer it yet. */
+static int xen_overlay_set_be_shinfo(uint64_t gfn)
+{
+ struct kvm_xen_hvm_attr xa = {
+ .type = KVM_XEN_ATTR_TYPE_SHARED_INFO,
+ .u.shared_info.gfn = gfn,
+ };
+
+ return kvm_vm_ioctl(kvm_state, KVM_XEN_HVM_SET_ATTR, &xa);
+}
+
+
+static void xen_overlay_realize(DeviceState *dev, Error **errp)
+{
+ XenOverlayState *s = XEN_OVERLAY(dev);
+
+ if (xen_mode != XEN_EMULATE) {
+ error_setg(errp, "Xen overlay page support is for Xen emulation");
+ return;
+ }
+
+ memory_region_init_ram(&s->shinfo_mem, OBJECT(dev), "xen:shared_info",
+ XEN_PAGE_SIZE, &error_abort);
+ memory_region_set_enabled(&s->shinfo_mem, true);
+
+ s->shinfo_ptr = memory_region_get_ram_ptr(&s->shinfo_mem);
+ s->shinfo_gpa = INVALID_GPA;
+ memset(s->shinfo_ptr, 0, XEN_PAGE_SIZE);
+}
+
+static int xen_overlay_post_load(void *opaque, int version_id)
+{
+ XenOverlayState *s = opaque;
+
+ if (s->shinfo_gpa != INVALID_GPA) {
+ xen_overlay_do_map_page(&s->shinfo_mem, s->shinfo_gpa);
+ xen_overlay_set_be_shinfo(s->shinfo_gpa >> XEN_PAGE_SHIFT);
+ }
+
+ return 0;
+}
+
+static bool xen_overlay_is_needed(void *opaque)
+{
+ return xen_mode == XEN_EMULATE;
+}
+
+static const VMStateDescription xen_overlay_vmstate = {
+ .name = "xen_overlay",
+ .version_id = 1,
+ .minimum_version_id = 1,
+ .needed = xen_overlay_is_needed,
+ .post_load = xen_overlay_post_load,
+ .fields = (VMStateField[]) {
+ VMSTATE_UINT64(shinfo_gpa, XenOverlayState),
+ VMSTATE_END_OF_LIST()
+ }
+};
+
+static void xen_overlay_reset(DeviceState *dev)
+{
+ kvm_xen_soft_reset();
+}
+
+static void xen_overlay_class_init(ObjectClass *klass, void *data)
+{
+ DeviceClass *dc = DEVICE_CLASS(klass);
+
+ dc->reset = xen_overlay_reset;
+ dc->realize = xen_overlay_realize;
+ dc->vmsd = &xen_overlay_vmstate;
+}
+
+static const TypeInfo xen_overlay_info = {
+ .name = TYPE_XEN_OVERLAY,
+ .parent = TYPE_SYS_BUS_DEVICE,
+ .instance_size = sizeof(XenOverlayState),
+ .class_init = xen_overlay_class_init,
+};
+
+void xen_overlay_create(void)
+{
+ xen_overlay_singleton = XEN_OVERLAY(sysbus_create_simple(TYPE_XEN_OVERLAY,
+ -1, NULL));
+}
+
+static void xen_overlay_register_types(void)
+{
+ type_register_static(&xen_overlay_info);
+}
+
+type_init(xen_overlay_register_types)
+
+int xen_overlay_map_shinfo_page(uint64_t gpa)
+{
+ XenOverlayState *s = xen_overlay_singleton;
+ int ret;
+
+ if (!s) {
+ return -ENOENT;
+ }
+
+ assert(qemu_mutex_iothread_locked());
+
+ if (s->shinfo_gpa) {
+ /* If removing shinfo page, turn the kernel magic off first */
+ ret = xen_overlay_set_be_shinfo(INVALID_GFN);
+ if (ret) {
+ return ret;
+ }
+ }
+
+ xen_overlay_do_map_page(&s->shinfo_mem, gpa);
+ if (gpa != INVALID_GPA) {
+ ret = xen_overlay_set_be_shinfo(gpa >> XEN_PAGE_SHIFT);
+ if (ret) {
+ return ret;
+ }
+ }
+ s->shinfo_gpa = gpa;
+
+ return 0;
+}
+
+void *xen_overlay_get_shinfo_ptr(void)
+{
+ XenOverlayState *s = xen_overlay_singleton;
+
+ if (!s) {
+ return NULL;
+ }
+
+ return s->shinfo_ptr;
+}
new file mode 100644
@@ -0,0 +1,20 @@
+/*
+ * QEMU Xen emulation: Shared/overlay pages 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_OVERLAY_H
+#define QEMU_XEN_OVERLAY_H
+
+void xen_overlay_create(void);
+
+int xen_overlay_map_shinfo_page(uint64_t gpa);
+void *xen_overlay_get_shinfo_ptr(void);
+
+#endif /* QEMU_XEN_OVERLAY_H */
@@ -12,6 +12,10 @@
#ifndef QEMU_SYSEMU_KVM_XEN_H
#define QEMU_SYSEMU_KVM_XEN_H
+/* The KVM API uses these to indicate "no GPA" or "no GFN" */
+#define INVALID_GPA UINT64_MAX
+#define INVALID_GFN UINT64_MAX
+
int kvm_xen_soft_reset(void);
uint32_t kvm_xen_get_caps(void);