linux-kernel - Re: [Xen-devel] [PATCH v2] [Bugfix] x86/apic: Fix xen IRQ allocation failure caused by commit b81975eade8c

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Date:	Tue, 13 Jan 2015 20:39:34 +0800
From:	Jiang Liu <jiang.liu@...ux.intel.com>
To:	David Vrabel <david.vrabel@...rix.com>,
	Sander Eikelenboom <linux@...elenboom.it>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Grant Likely <grant.likely@...aro.org>,
	Yinghai Lu <yinghai@...nel.org>
CC:	xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Subject: Re: [Xen-devel] [PATCH v2] [Bugfix] x86/apic: Fix xen IRQ allocation
 failure caused by commit b81975eade8c

On 2015/1/13 18:09, David Vrabel wrote:
> On 13/01/15 02:23, Jiang Liu wrote:
>> On 2015/1/12 23:01, David Vrabel wrote:
>>> On 12/01/15 13:39, Jiang Liu wrote:
>>>> Commit b81975eade8c ("x86, irq: Clean up irqdomain transition code")
>>>> breaks xen IRQ allocation because xen_smp_prepare_cpus() doesn't invoke
>>>> setup_IO_APIC(), so no irqdomains created for IOAPICs and
>>>> mp_map_pin_to_irq() fails at the very beginning.
>>>>
>>>> Enhance xen_smp_prepare_cpus() to call setup_IO_APIC() to initialize
>>>> irqdomain for IOAPICs.
>>>
>>> Having Xen call setup_IO_APIC() to initialize the irq domains then having to
>>> add special cases to it is just wrong.
>>>
>>> The bits of init deferred by mp_register_apic() are also deferred to
>>> two different places which looks odd.
>>>
>>> What about something like the following (untested) patch?
>> Hi David,
>> 	Really appreciate your suggestions about Xen IOAPIC:)
>> Your patch solves the issue, but it will break a coming patch
>> set to enable hierarchy irqdomain on x86.
> 
> For 3.19 I would recommend this patch.  Since it's been tested and it's
> pretty small.  Can you spin a version of this with a proper changelog.
> please?
Hi David,
	Good suggestion, I will send out the patch tomorrow.
Regards!
Gerry

> 
>> 	To enable hierarchy irqdomain on x86, need to build
>> irqdomains in following order:
>> 1) create irqdomain for CPU vector domain
>> 2) create irqdomains for interrupt remapping unit if interrupt
>>    remapping is enabled.
>> 3) create irqdomains for IOAPIC/MSI/HPET etc.
>>
>> Function arch_early_ioapic_init() is called before initializing
>> interrupt remapping subsystem. So creating IOAPIC irqdomains in
>> arch_early_ioapic_init() will break hierarchy irqdomain with
>> interrupt remapping enabled. I will post the x86 hierarchy
>> irqdomain patch soon.
>>
>> So could you please help to advice on:
> 
> I don't know enough about this area to comment on these authoritatively
> and I don't have time to look into this in more detail right now, but to
> the best of my understanding.
> 
>> 1) Is IOAPIC irqdomain needed for PV?
> 
> PV dom0 only requires a mechanism to obtain properties of the IOAPIC
> interrupt lines.  The actual physical interrupts are delivered to the
> hypervisor.  It doesn't require any of the irq setup.
> 
>> 2) Is IOAPIC irqdomain needed for HVM?
> 
> Yes.
> 
>> 3) Is IOAPIC irqdomain needed for Dom0?
> 
> 
> See (1) above.
> 
>> 4) What's the proper hook point to create IOAPIC irqdomain for Xen
>>    UP systems?
> 
> Don't know.
> 
> David
> 
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