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[Qemu-devel] [PATCH v2 1/2] hw/acpi/vmgenid: prevent device realization


From: Laszlo Ersek
Subject: [Qemu-devel] [PATCH v2 1/2] hw/acpi/vmgenid: prevent device realization on pre-2.5 machine types
Date: Mon, 20 Mar 2017 18:05:56 +0100

The WRITE_POINTER linker/loader command that underlies VMGENID depends on
commit baf2d5bfbac0 ("fw-cfg: support writeable blobs", 2017-01-12), which
in turn depends on fw_cfg DMA.

DMA for fw_cfg is enabled in 2.5+ machine types only (see commit
e6915b5f3a87, "fw_cfg: unbreak migration compatibility for 2.4 and earlier
machines", 2016-02-18).

Cc: "Michael S. Tsirkin" <address@hidden>
Cc: Ben Warren <address@hidden>
Cc: Igor Mammedov <address@hidden>
Cc: Paolo Bonzini <address@hidden>
Signed-off-by: Laszlo Ersek <address@hidden>
---

Notes:
    v2:
    - disable/enable vmgenid exactly in parallel with DMA support for fw_cfg
      [Michael, Paolo]

 include/hw/acpi/vmgenid.h |  1 +
 include/hw/compat.h       |  4 ++++
 hw/acpi/vmgenid.c         | 14 ++++++++++++++
 3 files changed, 19 insertions(+)

diff --git a/include/hw/acpi/vmgenid.h b/include/hw/acpi/vmgenid.h
index db7fa0e63303..8578476baebe 100644
--- a/include/hw/acpi/vmgenid.h
+++ b/include/hw/acpi/vmgenid.h
@@ -21,6 +21,7 @@ typedef struct VmGenIdState {
     DeviceClass parent_obj;
     QemuUUID guid;                /* The 128-bit GUID seen by the guest */
     uint8_t vmgenid_addr_le[8];   /* Address of the GUID (little-endian) */
+    bool write_pointer_available;
 } VmGenIdState;
 
 static inline Object *find_vmgenid_dev(void)
diff --git a/include/hw/compat.h b/include/hw/compat.h
index fc8c3e060007..5d5be91daf59 100644
--- a/include/hw/compat.h
+++ b/include/hw/compat.h
@@ -131,6 +131,10 @@
         .driver   = "fw_cfg_io",\
         .property = "dma_enabled",\
         .value    = "off",\
+    },{\
+        .driver   = "vmgenid",\
+        .property = "x-write-pointer-available",\
+        .value    = "off",\
     },
 
 #define HW_COMPAT_2_3 \
diff --git a/hw/acpi/vmgenid.c b/hw/acpi/vmgenid.c
index 7a3ad17d66ef..c3ddcc8e7cb0 100644
--- a/hw/acpi/vmgenid.c
+++ b/hw/acpi/vmgenid.c
@@ -205,9 +205,22 @@ static void vmgenid_handle_reset(void *opaque)
     memset(vms->vmgenid_addr_le, 0, ARRAY_SIZE(vms->vmgenid_addr_le));
 }
 
+static Property vmgenid_properties[] = {
+    DEFINE_PROP_BOOL("x-write-pointer-available", VmGenIdState,
+                     write_pointer_available, true),
+    DEFINE_PROP_END_OF_LIST(),
+};
+
 static void vmgenid_realize(DeviceState *dev, Error **errp)
 {
     VmGenIdState *vms = VMGENID(dev);
+
+    if (!vms->write_pointer_available) {
+        error_setg(errp, "%s requires DMA write support in fw_cfg, "
+                   "which this machine type does not provide", VMGENID_DEVICE);
+        return;
+    }
+
     qemu_register_reset(vmgenid_handle_reset, vms);
 }
 
@@ -218,6 +231,7 @@ static void vmgenid_device_class_init(ObjectClass *klass, 
void *data)
     dc->vmsd = &vmstate_vmgenid;
     dc->realize = vmgenid_realize;
     dc->hotpluggable = false;
+    dc->props = vmgenid_properties;
 
     object_class_property_add_str(klass, VMGENID_GUID, NULL,
                                   vmgenid_set_guid, NULL);
-- 
2.9.3





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