[RFC PATCH v2 03/22] i386/xen: Add xen-version machine property and init KVM Xen support

[David Woodhouse]

From: David Woodhouse <dwmw@amazon.co.uk>

This is a machine property for two main reasons. One is that it allows
us to set it in default_machine_opts for the xenfv platform when not
running on actual Xen. The other is that theoretically we *could* do
this with TCG too; we'd just have to implement a bunch of the stuff that
KVM already does for us.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
---
 hw/i386/pc.c            | 32 +++++++++++++++++++++++++++
 hw/i386/pc_piix.c       | 10 +++++++--
 include/hw/i386/pc.h    |  3 +++
 target/i386/kvm/kvm.c   | 26 ++++++++++++++++++++++
 target/i386/meson.build |  1 +
 target/i386/xen.c       | 49 +++++++++++++++++++++++++++++++++++++++++
 target/i386/xen.h       | 19 ++++++++++++++++
 7 files changed, 138 insertions(+), 2 deletions(-)
 create mode 100644 target/i386/xen.c
 create mode 100644 target/i386/xen.h

diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index 546b703cb4..9bada1a8ff 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -1811,6 +1811,32 @@ static void pc_machine_set_max_fw_size(Object *obj, 
Visitor *v,
     pcms->max_fw_size = value;
 }
 
+static void pc_machine_get_xen_version(Object *obj, Visitor *v,
+                                       const char *name, void *opaque,
+                                       Error **errp)
+{
+    PCMachineState *pcms = PC_MACHINE(obj);
+    uint32_t value = pcms->xen_version;
+
+    visit_type_uint32(v, name, &value, errp);
+}
+
+static void pc_machine_set_xen_version(Object *obj, Visitor *v,
+                                       const char *name, void *opaque,
+                                       Error **errp)
+{
+    PCMachineState *pcms = PC_MACHINE(obj);
+    Error *error = NULL;
+    uint32_t value;
+
+    visit_type_uint32(v, name, &value, &error);
+    if (error) {
+        error_propagate(errp, error);
+        return;
+    }
+
+    pcms->xen_version = value;
+}
 
 static void pc_machine_initfn(Object *obj)
 {
@@ -1978,6 +2004,12 @@ static void pc_machine_class_init(ObjectClass *oc, void 
*data)
         NULL, NULL);
     object_class_property_set_description(oc, PC_MACHINE_SMBIOS_EP,
         "SMBIOS Entry Point type [32, 64]");
+
+    object_class_property_add(oc, "xen-version", "uint32",
+        pc_machine_get_xen_version, pc_machine_set_xen_version,
+        NULL, NULL);
+    object_class_property_set_description(oc, "xen-version",
+        "Xen version to be emulated (in XENVER_version form e.g. 0x4000a for 
4.10)");
 }
 
 static const TypeInfo pc_machine_info = {
diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
index 0ad0ed1603..13286d0739 100644
--- a/hw/i386/pc_piix.c
+++ b/hw/i386/pc_piix.c
@@ -876,7 +876,10 @@ static void xenfv_4_2_machine_options(MachineClass *m)
     pc_i440fx_4_2_machine_options(m);
     m->desc = "Xen Fully-virtualized PC";
     m->max_cpus = HVM_MAX_VCPUS;
-    m->default_machine_opts = "accel=xen,suppress-vmdesc=on";
+    if (xen_enabled())
+            m->default_machine_opts = "accel=xen,suppress-vmdesc=on";
+    else
+            m->default_machine_opts = "accel=kvm,xen-version=0x40002";
 }
 
 DEFINE_PC_MACHINE(xenfv_4_2, "xenfv-4.2", pc_xen_hvm_init,
@@ -888,7 +891,10 @@ static void xenfv_3_1_machine_options(MachineClass *m)
     m->desc = "Xen Fully-virtualized PC";
     m->alias = "xenfv";
     m->max_cpus = HVM_MAX_VCPUS;
-    m->default_machine_opts = "accel=xen,suppress-vmdesc=on";
+    if (xen_enabled())
+            m->default_machine_opts = "accel=xen,suppress-vmdesc=on";
+    else
+            m->default_machine_opts = "accel=kvm,xen-version=0x30001";
 }
 
 DEFINE_PC_MACHINE(xenfv, "xenfv-3.1", pc_xen_hvm_init,
diff --git a/include/hw/i386/pc.h b/include/hw/i386/pc.h
index c95333514e..9b14b18836 100644
--- a/include/hw/i386/pc.h
+++ b/include/hw/i386/pc.h
@@ -52,6 +52,9 @@ typedef struct PCMachineState {
     bool default_bus_bypass_iommu;
     uint64_t max_fw_size;
 
+    /* Xen HVM emulation */
+    uint32_t xen_version;
+
     /* ACPI Memory hotplug IO base address */
     hwaddr memhp_io_base;
 
diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
index a213209379..0a2069b117 100644
--- a/target/i386/kvm/kvm.c
+++ b/target/i386/kvm/kvm.c
@@ -31,6 +31,7 @@
 #include "sysemu/runstate.h"
 #include "kvm_i386.h"
 #include "sev.h"
+#include "xen.h"
 #include "hyperv.h"
 #include "hyperv-proto.h"
 
@@ -774,6 +775,17 @@ static inline bool freq_within_bounds(int freq, int 
target_freq)
         return false;
 }
 
+static uint32_t kvm_arch_xen_version(MachineState *ms)
+{
+    uint32_t v = object_property_get_int(OBJECT(ms), "xen-version", NULL);
+
+    /* If it was unset, return zero */
+    if (v == (uint32_t) -1)
+            return 0;
+
+    return v;
+}
+
 static int kvm_arch_set_tsc_khz(CPUState *cs)
 {
     X86CPU *cpu = X86_CPU(cs);
@@ -2459,6 +2471,7 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
 {
     uint64_t identity_base = 0xfffbc000;
     uint64_t shadow_mem;
+    uint32_t xen_version;
     int ret;
     struct utsname utsname;
     Error *local_err = NULL;
@@ -2513,6 +2526,19 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
         }
     }
 
+    xen_version = kvm_arch_xen_version(ms);
+    if (xen_version) {
+#ifdef CONFIG_XEN_EMU
+            ret = kvm_xen_init(s, xen_version);
+            if (ret < 0) {
+                    return ret;
+            }
+#else
+            error_report("kvm: Xen support not enabled in qemu");
+            return -ENOTSUP;
+#endif
+    }
+
     ret = kvm_get_supported_msrs(s);
     if (ret < 0) {
         return ret;
diff --git a/target/i386/meson.build b/target/i386/meson.build
index ae38dc9563..9f3ef246b8 100644
--- a/target/i386/meson.build
+++ b/target/i386/meson.build
@@ -7,6 +7,7 @@ i386_ss.add(files(
   'cpu-dump.c',
 ))
 i386_ss.add(when: 'CONFIG_SEV', if_true: files('host-cpu.c'))
+i386_ss.add(when: 'CONFIG_XEN_EMU', if_true: files('xen.c'))
 
 # x86 cpu type
 i386_ss.add(when: 'CONFIG_KVM', if_true: files('host-cpu.c'))
diff --git a/target/i386/xen.c b/target/i386/xen.c
new file mode 100644
index 0000000000..bc183dce4e
--- /dev/null
+++ b/target/i386/xen.c
@@ -0,0 +1,49 @@
+/*
+ * Xen HVM emulation support in KVM
+ *
+ * Copyright © 2019 Oracle and/or its affiliates. All rights reserved.
+ * Copyright © 2022 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ * 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 "kvm/kvm_i386.h"
+#include "xen.h"
+
+int kvm_xen_init(KVMState *s, uint32_t xen_version)
+{
+    const int required_caps = KVM_XEN_HVM_CONFIG_HYPERCALL_MSR |
+        KVM_XEN_HVM_CONFIG_INTERCEPT_HCALL | KVM_XEN_HVM_CONFIG_SHARED_INFO;
+    struct kvm_xen_hvm_config cfg = {
+        .msr = XEN_HYPERCALL_MSR,
+        .flags = KVM_XEN_HVM_CONFIG_INTERCEPT_HCALL,
+    };
+    int xen_caps, ret;
+
+    xen_caps = kvm_check_extension(s, KVM_CAP_XEN_HVM);
+    if (required_caps & ~xen_caps) {
+        error_report("kvm: Xen HVM guest support not present or insufficient");
+        return -ENOSYS;
+    }
+
+    if (xen_caps & KVM_XEN_HVM_CONFIG_EVTCHN_SEND) {
+        struct kvm_xen_hvm_attr ha = {
+            .type = KVM_XEN_ATTR_TYPE_XEN_VERSION,
+            .u.xen_version = xen_version,
+        };
+        (void)kvm_vm_ioctl(s, KVM_XEN_HVM_SET_ATTR, &ha);
+
+        cfg.flags |= KVM_XEN_HVM_CONFIG_EVTCHN_SEND;
+    }
+
+    ret = kvm_vm_ioctl(s, KVM_XEN_HVM_CONFIG, &cfg);
+    if (ret < 0) {
+        error_report("kvm: Failed to enable Xen HVM support: %s", 
strerror(-ret));
+        return ret;
+    }
+
+    return 0;
+}
diff --git a/target/i386/xen.h b/target/i386/xen.h
new file mode 100644
index 0000000000..6c4f3b7822
--- /dev/null
+++ b/target/i386/xen.h
@@ -0,0 +1,19 @@
+/*
+ * Xen HVM emulation support in KVM
+ *
+ * Copyright © 2019 Oracle and/or its affiliates. All rights reserved.
+ * Copyright © 2022 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ * 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_I386_XEN_H
+#define QEMU_I386_XEN_H
+
+#define XEN_HYPERCALL_MSR 0x40000000
+
+int kvm_xen_init(KVMState *s, uint32_t xen_version);
+
+#endif /* QEMU_I386_XEN_H */
-- 
2.35.3