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 16:06:57 +0800
From:   Dou Liyang <douly.fnst@...fujitsu.com>
To:     Baoquan He <bhe@...hat.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



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

> 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)
>>>
>>
>>
> 
> 
>