linux-kernel - Re: [PATCH v6] KVM: x86: Add x2APIC "features" to control EOI broadcast suppression

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Message-ID: <feb11efd6bfbc5e7d5f6f430f40d4df5544f1d39.camel@infradead.org>
Date: Tue, 27 Jan 2026 13:09:04 -0800
From: David Woodhouse <dwmw2@...radead.org>
To: Khushit Shah <khushit.shah@...anix.com>, seanjc@...gle.com, 
	pbonzini@...hat.com, kai.huang@...el.com
Cc: mingo@...hat.com, x86@...nel.org, bp@...en8.de, hpa@...or.com, 
 linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
 dave.hansen@...ux.intel.com,  tglx@...utronix.de, jon@...anix.com,
 shaju.abraham@...anix.com,  stable@...r.kernel.org
Subject: Re: [PATCH v6] KVM: x86: Add x2APIC "features" to control EOI
 broadcast suppression

On Fri, 2026-01-23 at 12:56 +0000, Khushit Shah wrote:
> 
> @@ -4931,6 +4933,8 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>  		break;
>  	case KVM_CAP_X2APIC_API:
>  		r = KVM_X2APIC_API_VALID_FLAGS;
> +		if (kvm && !irqchip_split(kvm))
> +			r &= ~KVM_X2APIC_ENABLE_SUPPRESS_EOI_BROADCAST;
>  		break;
>  	case KVM_CAP_NESTED_STATE:
>  		r = kvm_x86_ops.nested_ops->get_state ?
> @@ -6748,11 +6752,24 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
>  		if (cap->args[0] & ~KVM_X2APIC_API_VALID_FLAGS)
>  			break;
>  
> +		if ((cap->args[0] & KVM_X2APIC_ENABLE_SUPPRESS_EOI_BROADCAST) &&
> +		    (cap->args[0] & KVM_X2APIC_DISABLE_SUPPRESS_EOI_BROADCAST))
> +			break;
> +
> +		if ((cap->args[0] & KVM_X2APIC_ENABLE_SUPPRESS_EOI_BROADCAST) &&
> +		    !irqchip_split(kvm))
> +			break;
> +
>  		if (cap->args[0] & KVM_X2APIC_API_USE_32BIT_IDS)

Is it possible to set KVM_X2APIC_ENABLE_SUPPRESS_EOI_BROADCAST and
*then* create the in-kernel I/O APIC?

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