[{"id":3678807,"web_url":"http://patchwork.ozlabs.org/comment/3678807/","msgid":"<232BE8D6-20C3-466F-972C-62CA540B6459@unpredictable.fr>","list_archive_url":null,"date":"2026-04-17T15:49:06","subject":"Re: [PATCH RFC v1 1/1] hw/s390x/ccw: Disable legacy virtio-pci by\n default (v11.1+)","submitter":{"id":91318,"url":"http://patchwork.ozlabs.org/api/people/91318/","name":"Mohamed Mediouni","email":"mohamed@unpredictable.fr"},"content":"> On 17. Apr 2026, at 17:43, Jaehoon Kim wrote:\n> \n> On the s390 Linux kernel, IO_SPACE_LIMIT has been 0 since the initial\n> zPCI implementation (commit cd24834130ac \"s390/pci: base support\"),\n> making I/O BARs unusable.\n> \n> However, when virtio-pci devices operate in transitional mode, QEMU\n> unconditionally exposes the legacy interface via BAR0. This results in\n> firmware warnings during PCI enumeration, such as:\n> \n> pci 0005:00:00.0: [Firmware Bug]: BAR 0: invalid; can't size\n> \n> even though BAR0 is never usable on the s390 kernel.\n> \n> Close this gap by disabling legacy virtio-pci support starting from\n> machine version 11.1. This effectively makes virtio-pci devices\n> non-transitional and prevents the creation of the unusable legacy I/O\n> BAR.\n> \n> This introduces s390x-specific global compatibility properties that\n> set disable-legacy=on as the default for virtio-pci devices. Machine\n> versions v11.0 and earlier set disable-legacy=off to maintain their\n> original default behavior (legacy support enabled), ensuring VMs\n> created with those versions continue to work identically.\n> \n> Users can override the default on the command line if needed:\n> - On v11.1+: -global virtio-pci.disable-legacy=off (to enable legacy)\n> - On v11.0-: -global virtio-pci.disable-legacy=on (to disable legacy)\n> \n> Signed-off-by: Jaehoon Kim \n\nReviewed-by: Mohamed Mediouni \n> ---\n> hw/s390x/s390-virtio-ccw.c | 23 +++++++++++++++++++++++\n> 1 file changed, 23 insertions(+)\n> \n> diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c\n> index cc768daeb0..6fbea1e289 100644\n> --- a/hw/s390x/s390-virtio-ccw.c\n> +++ b/hw/s390x/s390-virtio-ccw.c\n> @@ -788,6 +788,18 @@ static void machine_set_loadparm(Object *obj, Visitor *v,\n> g_free(val);\n> }\n> \n> +/*\n> + * S390x-specific global compatibility properties.\n> + *\n> + * Set disable-legacy=on as the default for virtio-pci devices starting\n> + * from v11.1. Machine versions v11.0 and earlier set disable-legacy=off\n> + * to maintain their original default behavior (legacy support enabled).\n> + */\n> +static GlobalProperty hw_compat_s390x[] = {\n> + { TYPE_VIRTIO_PCI, \"disable-legacy\", \"on\", .optional = true},\n> +};\n> +static const size_t hw_compat_s390x_len = G_N_ELEMENTS(hw_compat_s390x);\n> +\n> static void ccw_machine_class_init(ObjectClass *oc, const void *data)\n> {\n> MachineClass *mc = MACHINE_CLASS(oc);\n> @@ -878,6 +890,9 @@ static const TypeInfo ccw_machine_info = {\n> const void *data) \\\n> { \\\n> MachineClass *mc = MACHINE_CLASS(oc); \\\n> + /* Apply global s390x-wide default properties */ \\\n> + compat_props_add(mc->compat_props, hw_compat_s390x, \\\n> + hw_compat_s390x_len); \\\n> MACHINE_VER_SYM(class_options, ccw, __VA_ARGS__)(mc); \\\n> mc->desc = \"Virtual s390x machine (version \" MACHINE_VER_STR(__VA_ARGS__) \")\"; \\\n> mc->init = MACHINE_VER_SYM(mach_init, ccw, __VA_ARGS__); \\\n> @@ -923,7 +938,15 @@ static void ccw_machine_11_0_instance_options(MachineState *machine)\n> \n> static void ccw_machine_11_0_class_options(MachineClass *mc)\n> {\n> + /*\n> + * Preserve v11.0 and older version behavior:\n> + * keep legacy virtio-pci enabled.\n> + */\n> + static GlobalProperty compat[] = {\n> + { TYPE_VIRTIO_PCI, \"disable-legacy\", \"off\" },\n> + };\n> ccw_machine_11_1_class_options(mc);\n> + compat_props_add(mc->compat_props, compat, G_N_ELEMENTS(compat));\n> compat_props_add(mc->compat_props, hw_compat_11_0, hw_compat_11_0_len);\n> }\n> DEFINE_CCW_MACHINE(11, 0);\n> -- \n> 2.50.1\n> \n>","headers":{"Return-Path":"","X-Original-To":"incoming@patchwork.ozlabs.org","Delivered-To":"patchwork-incoming@legolas.ozlabs.org","Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=unpredictable.fr header.i=@unpredictable.fr\n header.a=rsa-sha256 header.s=sig1 header.b=fUuw4i/8;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=nongnu.org\n (client-ip=209.51.188.17; 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