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[RFC PATCH v4 14/47] hw/xen: Add xen_overlay device for emulating shared
From: |
David Woodhouse |
Subject: |
[RFC PATCH v4 14/47] hw/xen: Add xen_overlay device for emulating shared xenheap pages |
Date: |
Wed, 21 Dec 2022 01:05:50 +0000 |
From: David Woodhouse <dwmw@amazon.co.uk>
For the shared info page and for grant tables, Xen shares its own pages
from the "Xen heap" to the guest. The guest requests that a given page
from a certain address space (XENMAPSPACE_shared_info, etc.) be mapped
to a given GPA using the XENMEM_add_to_physmap hypercall.
To support that in qemu when *emulating* Xen, create a memory region
(migratable) and allow it to be mapped as an overlay when requested.
Xen theoretically allows the same page to be mapped multiple times
into the guest, but that's hard to track and reinstate over migration,
so we automatically *unmap* any previous mapping when creating a new
one. This approach has been used in production with.... a non-trivial
number of guests expecting true Xen, without any problems yet being
noticed.
This adds just the shared info page for now. The grant tables will be
a larger region, and will need to be overlaid one page at a time. I
think that means I need to create separate aliases for each page of
the overall grant_frames region, so that they can be mapped individually.
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
---
hw/i386/kvm/meson.build | 1 +
hw/i386/kvm/xen_overlay.c | 200 ++++++++++++++++++++++++++++++++++++++
hw/i386/kvm/xen_overlay.h | 20 ++++
include/sysemu/kvm_xen.h | 4 +
4 files changed, 225 insertions(+)
create mode 100644 hw/i386/kvm/xen_overlay.c
create mode 100644 hw/i386/kvm/xen_overlay.h
diff --git a/hw/i386/kvm/meson.build b/hw/i386/kvm/meson.build
index 95467f1ded..6165cbf019 100644
--- a/hw/i386/kvm/meson.build
+++ b/hw/i386/kvm/meson.build
@@ -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)
diff --git a/hw/i386/kvm/xen_overlay.c b/hw/i386/kvm/xen_overlay.c
new file mode 100644
index 0000000000..331dea6b8b
--- /dev/null
+++ b/hw/i386/kvm/xen_overlay.c
@@ -0,0 +1,200 @@
+/*
+ * 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_map_page_locked(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_map_page_locked(&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_class_init(ObjectClass *klass, void *data)
+{
+ DeviceClass *dc = DEVICE_CLASS(klass);
+
+ 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;
+ }
+
+ qemu_mutex_lock_iothread();
+ if (s->shinfo_gpa) {
+ /* If removing shinfo page, turn the kernel magic off first */
+ ret = xen_overlay_set_be_shinfo(INVALID_GFN);
+ if (ret) {
+ goto out;
+ }
+ }
+
+ xen_overlay_map_page_locked(&s->shinfo_mem, gpa);
+ if (gpa != INVALID_GPA) {
+ ret = xen_overlay_set_be_shinfo(gpa >> XEN_PAGE_SHIFT);
+ if (ret) {
+ goto out;
+ }
+ }
+ s->shinfo_gpa = gpa;
+ out:
+ qemu_mutex_unlock_iothread();
+
+ return ret;
+}
+
+void *xen_overlay_get_shinfo_ptr(void)
+{
+ XenOverlayState *s = xen_overlay_singleton;
+
+ if (!s) {
+ return NULL;
+ }
+
+ return s->shinfo_ptr;
+}
diff --git a/hw/i386/kvm/xen_overlay.h b/hw/i386/kvm/xen_overlay.h
new file mode 100644
index 0000000000..00cff05bb0
--- /dev/null
+++ b/hw/i386/kvm/xen_overlay.h
@@ -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 */
diff --git a/include/sysemu/kvm_xen.h b/include/sysemu/kvm_xen.h
index 296533f2d5..3e43cd7843 100644
--- a/include/sysemu/kvm_xen.h
+++ b/include/sysemu/kvm_xen.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
+
uint32_t kvm_xen_get_caps(void);
#define kvm_xen_has_cap(cap) (!!(kvm_xen_get_caps() & \
--
2.35.3
- [RFC PATCH v4 01/47] Xen HVM support under KVM, David Woodhouse, 2022/12/20
- [RFC PATCH v4 15/47] i386/xen: add pc_machine_kvm_type to initialize XEN_EMULATE mode, David Woodhouse, 2022/12/20
- [RFC PATCH v4 19/47] i386/xen: implement HYPERVISOR_hvm_op, David Woodhouse, 2022/12/20
- [RFC PATCH v4 11/47] i386/xen: implement HYPERVISOR_xen_version, David Woodhouse, 2022/12/20
- [RFC PATCH v4 44/47] hw/xen: Support mapping grant frames, David Woodhouse, 2022/12/20
- [RFC PATCH v4 24/47] i386/xen: implement HYPERVISOR_event_channel_op, David Woodhouse, 2022/12/20
- [RFC PATCH v4 14/47] hw/xen: Add xen_overlay device for emulating shared xenheap pages,
David Woodhouse <=
- [RFC PATCH v4 41/47] hw/xen: Support HVM_PARAM_CALLBACK_TYPE_PCI_INTX callback, David Woodhouse, 2022/12/20
- [RFC PATCH v4 01/47] include: import Xen public headers to include/standard-headers/, David Woodhouse, 2022/12/20
- [RFC PATCH v4 05/47] i386/kvm: handle Xen HVM cpuid leaves, David Woodhouse, 2022/12/20
- [RFC PATCH v4 21/47] i386/xen: handle VCPUOP_register_vcpu_info, David Woodhouse, 2022/12/20
- [RFC PATCH v4 13/47] i386/xen: Implement SCHEDOP_poll and SCHEDOP_yield, David Woodhouse, 2022/12/20
- [RFC PATCH v4 12/47] i386/xen: implement HYPERVISOR_sched_op, SCHEDOP_shutdown, David Woodhouse, 2022/12/20
- [RFC PATCH v4 35/47] hw/xen: Implement EVTCHNOP_alloc_unbound, David Woodhouse, 2022/12/20
- [RFC PATCH v4 03/47] xen: Add XEN_DISABLED mode and make it default, David Woodhouse, 2022/12/20
- [RFC PATCH v4 37/47] hw/xen: Implement EVTCHNOP_bind_vcpu, David Woodhouse, 2022/12/20