Re: [Qemu-devel] [PATCH v2 1/2] hw/acpi/vmgenid: prevent device realization on pre-2.5 machine types

[Ben Warren]

> On Mar 20, 2017, at 10:05 AM, Laszlo Ersek <address@hidden> wrote:
> 
> 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>
Reviewed-by: Ben Warren <address@hidden <mailto: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
> 
>