Re: [PATCH] KVM: x86: deprecate -M kernel-irqchip=off except for -M isapc

[Maxim Levitsky <mlevitsk@redhat.com>]

On Mon, 2021-03-01 at 12:17 +0100, Paolo Bonzini wrote:
> The userspace local APIC is basically untested and does not support many
> features such as TSC deadline timer, x2APIC or PV spinlocks.  On the
> other hand, the PIT and IOAPIC are okay as they are not tied to
> the processor and are tested with -M kernel-irqchip=split.
> 
> Therefore, deprecate the local APIC and, with it, limit
> -M kernel-irqchip=off to the ISA PC machine type, which does not
> have a local APIC at all.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>

Best regards,
	Maxim Levitsky

> ---
>  docs/system/deprecated.rst | 7 +++++++
>  hw/intc/apic.c             | 5 +++++
>  2 files changed, 12 insertions(+)
> 
> diff --git a/docs/system/deprecated.rst b/docs/system/deprecated.rst
> index 561c916da2..ae180dc887 100644
> --- a/docs/system/deprecated.rst
> +++ b/docs/system/deprecated.rst
> @@ -153,6 +153,13 @@ The ``-writeconfig`` option is not able to serialize the entire contents
>  of the QEMU command line.  It is thus considered a failed experiment
>  and deprecated, with no current replacement.
>  
> +Userspace local APIC with KVM (x86, since 6.0)
> +'''''''''''''''''''''''''''''''''''''''''
> +
> +Using ``-M kernel-irqchip=off`` with x86 machine types that include a local
> +APIC is deprecated.  The ``split`` setting is supported, as is using
> +``-M kernel-irqchip=off`` with the ISA PC machine type.
> +
>  QEMU Machine Protocol (QMP) commands
>  ------------------------------------
>  
> diff --git a/hw/intc/apic.c b/hw/intc/apic.c
> index 3ada22f427..7e9601b89d 100644
> --- a/hw/intc/apic.c
> +++ b/hw/intc/apic.c
> @@ -875,6 +875,11 @@ static void apic_realize(DeviceState *dev, Error **errp)
>          return;
>      }
>  
> +    if (kvm_enabled()) {
> +        warn_report("Userspace local APIC is deprecated for KVM.");
> +        warn_report("Do not use kernel-irqchip except for the -M isapc machine type.");
> +    }
> +
>      memory_region_init_io(&s->io_memory, OBJECT(s), &apic_io_ops, s, "apic-msi",
>                            APIC_SPACE_SIZE);
>