Re: [PATCH v2] hw/i386: disable smbus migration for xenfv

[Olaf Hering <olaf@aepfle.de>]

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The approach below (making 'xenfv' an alias of 'pc') does not work:
xen_enabled() is false when pc_i440fx_3_1_machine_options runs.

So, how is this incompatibility between qemu2/3 and qemu4+ supposed to be fixed?
Using '-machine pc,accel=xen -device xen-platform' is incompatible with '-machine xenpv' because the platform device has a different PCI address. As such it is not migrateable.

Olaf

Am Mon, 27 Jan 2020 10:09:51 +0100
schrieb Olaf Hering <olaf@aepfle.de>:

> Am Mon, 20 Jan 2020 11:18:41 +0000
> schrieb Paul Durrant <pdurrant@gmail.com>:
> 
> > On Fri, 17 Jan 2020 at 13:06, Olaf Hering <olaf@aepfle.de> wrote:  
> > > What would future domUs lose if 'xenfv' would be locked to 'pc-i440fx-3.0'?  
> 
> > I guess eventually that pc type would be removed and then we'd have a
> > compat issue. Ideally I think libxl should simply not use xenfv and
> > then it can be deprecated and removed, and then such issues can be
> > dealt with directly in xl/libxl.  
> 
> I think this does not answer the question at all.
> What future versions of libxl do is one thing.
> What existing versions of libxl do with future versions of qemu is another.
> 
> 
> IMO it was wrong to map "xenfv" to "pc", simply because it entirely
> ignores live migration. We were just lucky until qemu-3.1. Maybe the
> creators of 'xenfv' just meant it to be "do everything to make it
> compatible with HVM".
> 
> What about a variant of this change, to lock 'xenfv' to 'qemu-3.0'?
> 
> 
> --- a/hw/i386/pc_piix.c
> +++ b/hw/i386/pc_piix.c
> @@ -490,6 +490,13 @@ static void pc_i440fx_3_0_machine_options(MachineClass *m)
>      pc_i440fx_3_1_machine_options(m);
>      compat_props_add(m->compat_props, hw_compat_3_0, hw_compat_3_0_len);
>      compat_props_add(m->compat_props, pc_compat_3_0, pc_compat_3_0_len);
> +
> +    m->alias = "xenfv";
> +    if (xen_enabled()) {
> +        m->desc = "Xen Fully-virtualized PC";
> +        m->max_cpus = HVM_MAX_VCPUS;
> +        m->default_machine_opts = "accel=xen";
> +    }
>  }
>  
>  DEFINE_I440FX_MACHINE(v3_0, "pc-i440fx-3.0", NULL,
> @@ -500,6 +507,7 @@ static void pc_i440fx_2_12_machine_options(MachineClass *m)
>      pc_i440fx_3_0_machine_options(m);
>      compat_props_add(m->compat_props, hw_compat_2_12, hw_compat_2_12_len);
>      compat_props_add(m->compat_props, pc_compat_2_12, pc_compat_2_12_len);
> +    m->alias = NULL;
>  }
>  
>  DEFINE_I440FX_MACHINE(v2_12, "pc-i440fx-2.12", NULL,
> @@ -946,14 +954,3 @@ DEFINE_PC_MACHINE(isapc, "isapc", pc_init_isa,
>                    isapc_machine_options);
>  
>  
> -#ifdef CONFIG_XEN
> -static void xenfv_machine_options(MachineClass *m)
> -{
> -    m->desc = "Xen Fully-virtualized PC";
> -    m->max_cpus = HVM_MAX_VCPUS;
> -    m->default_machine_opts = "accel=xen";
> -}
> -
> -DEFINE_PC_MACHINE(xenfv, "xenfv", pc_xen_hvm_init,
> -                  xenfv_machine_options);
> -#endif
> 
> 
> Olaf


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