Re: [PATCH 03/13] s390: move css_migration_enabled from machine to css.c

[Thomas Huth <thuth@redhat.com>]

On 09/05/2024 19.00, Paolo Bonzini wrote:
> The CSS subsystem uses global variables, just face the truth and use
> a variable also for whether the CSS vmstate is in use; remove the
> indirection of fetching it from the machine type, which makes the
> TCG code depend unnecessarily on the virtio-ccw machine.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>   include/hw/s390x/css.h             |  6 ++++++
>   include/hw/s390x/s390-virtio-ccw.h |  7 -------
>   hw/s390x/css.c                     | 10 +++++++---
>   hw/s390x/s390-virtio-ccw.c         | 15 +++------------
>   4 files changed, 16 insertions(+), 22 deletions(-)
> 
> diff --git a/include/hw/s390x/css.h b/include/hw/s390x/css.h
> index ba72ee3dd20..8289e458370 100644
> --- a/include/hw/s390x/css.h
> +++ b/include/hw/s390x/css.h
> @@ -333,4 +333,10 @@ static inline int ccw_dstream_read_buf(CcwDataStream *cds, void *buff, int len)
>   #define ccw_dstream_read(cds, v) ccw_dstream_read_buf((cds), &(v), sizeof(v))
>   #define ccw_dstream_write(cds, v) ccw_dstream_write_buf((cds), &(v), sizeof(v))
>   
> +/**
> + * true if (vmstate based) migration of the channel subsystem
> + * is enabled, false if it is disabled.
> + */
> +extern bool css_migration_enabled;
> +
>   #endif
> diff --git a/include/hw/s390x/s390-virtio-ccw.h b/include/hw/s390x/s390-virtio-ccw.h
> index c1d46e78af8..c0494e511cb 100644
> --- a/include/hw/s390x/s390-virtio-ccw.h
> +++ b/include/hw/s390x/s390-virtio-ccw.h
> @@ -43,7 +43,6 @@ struct S390CcwMachineClass {
>       /*< public >*/
>       bool ri_allowed;
>       bool cpu_model_allowed;
> -    bool css_migration_enabled;
>       bool hpage_1m_allowed;
>       int max_threads;
>   };
> @@ -55,10 +54,4 @@ bool cpu_model_allowed(void);
>   /* 1M huge page mappings allowed by the machine */
>   bool hpage_1m_allowed(void);
>   
> -/**
> - * Returns true if (vmstate based) migration of the channel subsystem
> - * is enabled, false if it is disabled.
> - */
> -bool css_migration_enabled(void);
> -
>   #endif
> diff --git a/hw/s390x/css.c b/hw/s390x/css.c
> index 295530963a6..b2d5327dbf4 100644
> --- a/hw/s390x/css.c
> +++ b/hw/s390x/css.c
> @@ -23,6 +23,8 @@
>   #include "hw/s390x/s390-virtio-ccw.h"
>   #include "hw/s390x/s390-ccw.h"
>   
> +bool css_migration_enabled = true;
> +
>   typedef struct CrwContainer {
>       CRW crw;
>       QTAILQ_ENTRY(CrwContainer) sibling;
> @@ -180,7 +182,7 @@ static const VMStateDescription vmstate_orb = {
>   
>   static bool vmstate_schdev_orb_needed(void *opaque)
>   {
> -    return css_migration_enabled();
> +    return css_migration_enabled;
>   }
>   
>   static const VMStateDescription vmstate_schdev_orb = {
> @@ -388,7 +390,7 @@ static int subch_dev_post_load(void *opaque, int version_id)
>           css_subch_assign(s->cssid, s->ssid, s->schid, s->devno, s);
>       }
>   
> -    if (css_migration_enabled()) {
> +    if (css_migration_enabled) {
>           /* No compat voodoo to do ;) */
>           return 0;
>       }
> @@ -412,7 +414,9 @@ static int subch_dev_post_load(void *opaque, int version_id)
>   
>   void css_register_vmstate(void)
>   {
> -    vmstate_register(NULL, 0, &vmstate_css, &channel_subsys);
> +    if (css_migration_enabled) {
> +        vmstate_register(NULL, 0, &vmstate_css, &channel_subsys);
> +    }
>   }
>   
>   IndAddr *get_indicator(hwaddr ind_addr, int len)
> diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
> index 1383e47eeb5..aa90703d518 100644
> --- a/hw/s390x/s390-virtio-ccw.c
> +++ b/hw/s390x/s390-virtio-ccw.c
> @@ -275,11 +275,9 @@ static void ccw_init(MachineState *machine)
>       s390_enable_css_support(s390_cpu_addr2state(0));
>   
>       ret = css_create_css_image(VIRTUAL_CSSID, true);
> -
>       assert(ret == 0);
> -    if (css_migration_enabled()) {
> -        css_register_vmstate();
> -    }
> +
> +    css_register_vmstate();
>   
>       /* Create VirtIO network adapters */
>       s390_create_virtio_net(BUS(css_bus), mc->default_nic);
> @@ -741,7 +739,6 @@ static void ccw_machine_class_init(ObjectClass *oc, void *data)
>   
>       s390mc->ri_allowed = true;
>       s390mc->cpu_model_allowed = true;
> -    s390mc->css_migration_enabled = true;
>       s390mc->hpage_1m_allowed = true;
>       s390mc->max_threads = 1;
>       mc->init = ccw_init;
> @@ -811,11 +808,6 @@ static const TypeInfo ccw_machine_info = {
>       },
>   };
>   
> -bool css_migration_enabled(void)
> -{
> -    return get_machine_class()->css_migration_enabled;
> -}
> -
>   #define DEFINE_CCW_MACHINE(suffix, verstr, latest)                            \
>       static void ccw_machine_##suffix##_class_init(ObjectClass *oc,            \
>                                                     void *data)                 \
> @@ -1171,7 +1163,6 @@ static void ccw_machine_2_9_instance_options(MachineState *machine)
>   
>   static void ccw_machine_2_9_class_options(MachineClass *mc)
>   {
> -    S390CcwMachineClass *s390mc = S390_CCW_MACHINE_CLASS(mc);
>       static GlobalProperty compat[] = {
>           { TYPE_S390_STATTRIB, "migration-enabled", "off", },
>           { TYPE_S390_FLIC_COMMON, "migration-enabled", "off", },
> @@ -1180,7 +1171,7 @@ static void ccw_machine_2_9_class_options(MachineClass *mc)
>       ccw_machine_2_10_class_options(mc);
>       compat_props_add(mc->compat_props, hw_compat_2_9, hw_compat_2_9_len);
>       compat_props_add(mc->compat_props, compat, G_N_ELEMENTS(compat));
> -    s390mc->css_migration_enabled = false;
> +    css_migration_enabled = false;
>   }
>   DEFINE_CCW_MACHINE(2_9, "2.9", false);

I think this is wrong: By adding this to ccw_machine_2_9_class_options the 
variable now always gets set to false, even for newer machines, since the 
*class_options functions are part of the "class_init" which is always done.
You have to add it to ccw_machine_2_9_instance_options() instead to make it 
work as expected.

  Thomas