linux-kernel - Re: [PATCH 4/5] x86/apic: Support 15 bits of APIC ID in IOAPIC/MSI where available

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Message-ID: <87h7r5vsog.fsf@nanos.tec.linutronix.de>
Date:   Thu, 08 Oct 2020 13:54:55 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     David Woodhouse <dwmw2@...radead.org>, x86@...nel.org
Cc:     kvm <kvm@...r.kernel.org>, Paolo Bonzini <pbonzini@...hat.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/5] x86/apic: Support 15 bits of APIC ID in IOAPIC/MSI where available

On Wed, Oct 07 2020 at 13:20, David Woodhouse wrote:
>  
> +	/*
> +	 * If the hypervisor supports extended destination ID in IOAPIC
> +	 * and MSI, that increases the maximum APIC ID that can be used
> +	 * for non-remapped IRQ domains.
> +	 */
> +	if (x86_init.hyper.msi_ext_dest_id()) {
> +		msi_ext_dest_id = 1;
> +		apic_limit = 32767;
> +	}

This needs to be outside of the remap mode check because?

> +
>  	if (remap_mode != IRQ_REMAP_X2APIC_MODE) {
>  		/*
>  		 * Using X2APIC without IR is not architecturally supported
> @@ -1856,9 +1868,10 @@ static __init void try_to_enable_x2apic(int remap_mode)
>  		 * in physical mode, and CPUs with an APIC ID that cannnot
>  		 * be addressed must not be brought online.
>  		 */
> -		x2apic_set_max_apicid(255);
> +		x2apic_set_max_apicid(apic_limit);
>  		x2apic_phys = 1;
>  	}
> +
>  	x2apic_enable();
>  }
>  
> diff --git a/arch/x86/kernel/apic/msi.c b/arch/x86/kernel/apic/msi.c
> index 2825e003259c..85206f971284 100644
> --- a/arch/x86/kernel/apic/msi.c
> +++ b/arch/x86/kernel/apic/msi.c
> @@ -23,8 +23,11 @@
>  
>  struct irq_domain *x86_pci_msi_default_domain __ro_after_init;
>  
> +int msi_ext_dest_id __ro_after_init;

bool please.

Aside of that this breaks the build for a kernel with CONFIG_PCI_MSI=n

Thanks,

        tglx