Re: [PATCH for-7.1] hw/mips/malta: turn off x86 specific features of PIIX4_PM

[Peter Maydell <peter.maydell@linaro.org>]

On Thu, 28 Jul 2022 at 12:50, Igor Mammedov <imammedo@redhat.com> wrote:
>
> QEMU crashes trying to save VMSTATE when only MIPS target are compiled in
>   $ qemu-system-mips -monitor stdio
>   (qemu) migrate "exec:gzip -c > STATEFILE.gz"
>   Segmentation fault (core dumped)
>
> It happens due to PIIX4_PM trying to parse hotplug vmstate structures
> which are valid only for x86 and not for MIPS (as it requires ACPI
> tables support which is not existent for ithe later)
>
> Issue was probably exposed by trying to cleanup/compile out unused
> ACPI bits from MIPS target (but forgetting about migration bits).
>
> Disable compiled out features using compat properties as the least
> risky way to deal with issue.
>
> Signed-off-by: Igor Mammedov <imammedo@redhat.com>

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/995

> ---
> PS:
> another approach could be setting defaults to disabled state and
> enabling them using compat props on PC machines (which is more
> code to deal with => more risky) or continue with PIIX4_PM
> refactoring to split x86-shism out (which I'm not really
> interested in due to risk of regressions for not much of
> benefit)
> ---
>  hw/mips/malta.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
>
> diff --git a/hw/mips/malta.c b/hw/mips/malta.c
> index 7a0ec513b0..0e932988e0 100644
> --- a/hw/mips/malta.c
> +++ b/hw/mips/malta.c
> @@ -1442,6 +1442,14 @@ static const TypeInfo mips_malta_device = {
>      .instance_init = mips_malta_instance_init,
>  };
>
> +GlobalProperty malta_compat[] = {
> +    { "PIIX4_PM", "memory-hotplug-support", "off" },
> +    { "PIIX4_PM", "acpi-pci-hotplug-with-bridge-support", "off" },
> +    { "PIIX4_PM", "acpi-root-pci-hotplug", "off" },
> +    { "PIIX4_PM", "x-not-migrate-acpi-index", "true" },
> +};

Is there an easy way to assert in hw/acpi/piix4.c that if
CONFIG_ACPI_PCIHP was not set then the board has initialized
all these properties to the don't-use-hotplug state ?
That would be a guard against similar bugs (though I suppose
we probably aren't likely to add new piix4 boards...)

> +const size_t malta_compat_len = G_N_ELEMENTS(malta_compat);
> +
>  static void mips_malta_machine_init(MachineClass *mc)
>  {
>      mc->desc = "MIPS Malta Core LV";
> @@ -1455,6 +1463,7 @@ static void mips_malta_machine_init(MachineClass *mc)
>      mc->default_cpu_type = MIPS_CPU_TYPE_NAME("24Kf");
>  #endif
>      mc->default_ram_id = "mips_malta.ram";
> +    compat_props_add(mc->compat_props, malta_compat, malta_compat_len);
>  }
>
>  DEFINE_MACHINE("malta", mips_malta_machine_init)
> --
> 2.31.1

thanks
-- PMM