linux-kernel - Re: [RESEND PATCH 3/3] x86/apic: Clean up the names of legacy irq mode setting related functions

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Date:   Fri, 19 Jan 2018 17:22:23 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Dou Liyang <douly.fnst@...fujitsu.com>
Cc:     linux-kernel@...r.kernel.org, mingo@...hat.com, tglx@...utronix.de,
        hpa@...or.com, x86@...nel.org, rostedt@...dmis.org,
        jgross@...e.com, peterz@...radead.org, uobergfe@...hat.com,
        joro@...tes.org
Subject: Re: [RESEND PATCH 3/3] x86/apic: Clean up the names of legacy irq
 mode setting related functions

On 01/19/18 at 04:06pm, Dou Liyang wrote:
> 
> 
> At 01/19/2018 03:21 PM, Baoquan He wrote:
> > On 01/19/18 at 02:42pm, Dou Liyang wrote:
> > > Hi Baoquan,
> > > 
> > > At 01/05/2018 12:39 PM, Baoquan He wrote:
> > > [...]
> > > >    /*
> > > > - * Not an __init, needed by kexec/kdump code.
> > > > - * For safety IO-APIC and Local APIC need be cleared before this.
> > > > + * In legacy irq mode, full DOS compatibility with the uniprocessor PC/AT is
> > > > + * provided by using the APICs in conjunction with standard 8259A-equivalent
> > > > + * programmable interrupt controllers (PICs). It's necessary to deliver legacy
> > > > + * interrupts even when APIC mode is not enabled. This is required by kexec/
> > > > + * kdump before enter into the 2nd kernel.
> > > >     */
> > > >    void switch_to_legacy_irq_mode(void)
> > > >    {
> > > >    	if (!nr_legacy_irqs())
> > > >    		return;
> > > > -	x86_io_apic_ops.disable();
> > > > +	ioapic_set_virtual_wire_mode();
> > > > +
> > > > +	if (boot_cpu_has(X86_FEATURE_APIC) || apic_from_smp_config())
> > > > +		lapic_set_legacy_irq_mode(ioapic_i8259.pin != -1);
> > > 
> > > Seems these two function, ioapic/lapic_set_legacy_irq_mode should be
> > > exclusive.
> > 
> > Thanks for looking into this, dou!
> > 
> > It might be not exclusive. You can see mp_spec 3.6.2.2 Virtual Wire Mode
> 
> Oops! Sorry to confuse you, here what I want to say is that the code
> make me think that we set through IO-APIC first, then set through
> Local-APIC then. But, we can be only in one mode of them.
> 
> Just worry about this code seems ignore the irq remapping situation.
> 
> We call switch_to_legacy_irq_mode() directly in machine_kexec(),
> why we also set x86_io_apic_ops:
> 
>   .disable = switch_to_legacy_irq_mode

You are right, this is not very clear. Since we call switch_to_legacy_irq_mode()
directly, nobody will call x86_io_apic_ops.disable() any more.

Should keep native_disable_io_apic() and let x86_io_apic_ops.disable()
to point at it.

Thanks
Baoquan
> 
> > subsection, there are two kinds of virtual wire mode, one is
> > 8259A-Equivalent pics is connected to lint0 of boot cpu LAPIC, the other
> > is 8259A-Equivalent pics go through IO-APIC, then is connected to lint0
> > of LAPIC. Whatever it is, LAPIC need be set as through-lapic.
> > 
> 
> Yes, Absolutely right!
> 
> > Above is what I got from mp_spec. But from function
> > native_disable_io_apic() and disconnect_bsp_APIC(), the code seems to be
> > telling that if io-apic is connected to 8259A-Equivalent pics, we need
> > mask lvt0 of LAPIC. This conflicts with mp_spec 3.6.2.2.
> > 
> 
> I think so.
> 
> Thanks,
> 	dou.
> > Thanks
> > Baoquan
> > > 
> > > But We do that because both the through-lapic and through-ioapic virtual
> > > wire mode need setup the APIC_SPIV_APIC_ENABLED which is only located in
> > > the lapic_set_legacy_irq_mode(). So we need call them both.
> > > 
> > > IMO, this cleanup may not make it clear. we can separate these two mode
> > > totally or just keep it like before.
> > > 
> > > Thanks,
> > > 	dou.
> > > >    }
> > > >    #ifdef CONFIG_X86_32
> > > > diff --git a/arch/x86/kernel/x86_init.c b/arch/x86/kernel/x86_init.c
> > > > index 1151ccd72ce9..c30f0f273dbd 100644
> > > > --- a/arch/x86/kernel/x86_init.c
> > > > +++ b/arch/x86/kernel/x86_init.c
> > > > @@ -148,5 +148,5 @@ void arch_restore_msi_irqs(struct pci_dev *dev)
> > > >    struct x86_io_apic_ops x86_io_apic_ops __ro_after_init = {
> > > >    	.read			= native_io_apic_read,
> > > > -	.disable		= native_disable_io_apic,
> > > > +	.disable		= switch_to_legacy_irq_mode,
> > > >    };
> > > > diff --git a/drivers/iommu/irq_remapping.c b/drivers/iommu/irq_remapping.c
> > > > index 49721b4e1975..751472ddf536 100644
> > > > --- a/drivers/iommu/irq_remapping.c
> > > > +++ b/drivers/iommu/irq_remapping.c
> > > > @@ -37,7 +37,7 @@ static void irq_remapping_disable_io_apic(void)
> > > >    	 * now.
> > > >    	 */
> > > >    	if (boot_cpu_has(X86_FEATURE_APIC) || apic_from_smp_config())
> > > > -		disconnect_bsp_APIC(0);
> > > > +		lapic_set_legacy_irq_mode(0);
> > > >    }
> > > >    static void __init irq_remapping_modify_x86_ops(void)
> > > > 
> > > 
> > > 
> > 
> > 
> > 
> 
>