Re: [PATCH for-6.1 v2] i386: do not call cpudef-only models functions for max, host, base

["Woodhouse, David" <dwmw@amazon.co.uk>]

On Fri, 2021-07-23 at 13:29 +0200, Claudio Fontana wrote:
>  static void kvm_cpu_instance_init(CPUState *cs)
>  {
>      X86CPU *cpu = X86_CPU(cs);
> +    X86CPUClass *xcc = X86_CPU_GET_CLASS(cpu);
>  
>      host_cpu_instance_init(cpu);
>  
> -    if (!kvm_irqchip_in_kernel()) {
> -        x86_cpu_change_kvm_default("x2apic", "off");
> -    } else if (kvm_irqchip_is_split() && kvm_enable_x2apic()) {
> -        x86_cpu_change_kvm_default("kvm-msi-ext-dest-id", "on");
> -    }
> -
> -    /* Special cases not set in the X86CPUDefinition structs: */
> +    if (xcc->model) {
> +        /* only applies to builtin_x86_defs cpus */
> +        if (!kvm_irqchip_in_kernel()) {
> +            x86_cpu_change_kvm_default("x2apic", "off");
> +        } else if (kvm_irqchip_is_split() && kvm_enable_x2apic()) {
> +            x86_cpu_change_kvm_default("kvm-msi-ext-dest-id", "on");
> +        }
>  
> -    x86_cpu_apply_props(cpu, kvm_default_props);
> +        /* Special cases not set in the X86CPUDefinition structs: */
> +        x86_cpu_apply_props(cpu, kvm_default_props);
> +    }
>  

I think this causes a regression in x2apic and kvm-msi-ext-dest-id
support. If you start qemu thus:

qemu-system-x86_64 -machine q35,accel=kvm,usb=off,kernel_irqchip=split -cpu host -smp 288,sockets=9,cores=16,threads=2

The guest now sees those features, but we don't actually call
kvm_enable_x2apic() so the APIC broadcast quirk doesn't get disabled,
and interrupts targeted at APIC ID 255 are interpreted as broadcasts:

[ 73.198504] __common_interrupt: 0.34 No irq handler for vector
[ 73.198515] __common_interrupt: 11.34 No irq handler for vector
[ 73.198517] __common_interrupt: 12.34 No irq handler for vector
[ 73.198521] __common_interrupt: 15.34 No irq handler for vector
[ 73.198524] __common_interrupt: 17.34 No irq handler for vector
[ 73.198528] __common_interrupt: 34.34 No irq handler for vector
[ 73.198529] __common_interrupt: 20.34 No irq handler for vector
[ 73.198533] __common_interrupt: 41.34 No irq handler for vector
[ 73.198539] __common_interrupt: 27.34 No irq handler for vector
[ 73.198542] __common_interrupt: 28.34 No irq handler for vector



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