linux-kernel - Re: [PATCH v5 10/12] x86/xen: Bypass intr mode setup in enlighten

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Date:   Mon, 3 Jul 2017 15:17:53 +0800
From:   Dou Liyang <douly.fnst@...fujitsu.com>
To:     Thomas Gleixner <tglx@...utronix.de>
CC:     <x86@...nel.org>, <linux-kernel@...r.kernel.org>,
        <xen-devel@...ts.xenproject.org>, <mingo@...nel.org>,
        <hpa@...or.com>, <ebiederm@...ssion.com>, <bhe@...hat.com>,
        <boris.ostrovsky@...cle.com>, <peterz@...radead.org>,
        <izumi.taku@...fujitsu.com>
Subject: Re: [PATCH v5 10/12] x86/xen: Bypass intr mode setup in enlighten_pv
 system

Hi Thomas,

At 07/03/2017 02:56 PM, Thomas Gleixner wrote:
> On Mon, 3 Jul 2017, Dou Liyang wrote:
>> At 07/03/2017 03:18 AM, Thomas Gleixner wrote:
>>> On Fri, 30 Jun 2017, Dou Liyang wrote:
>>>
>>>> xen_smp_ops overwrites smp_prepare_cpus to xen_pv_smp_prepare_cpus
>>>> which initializes interrupt itself.
>>>>
>>>> Touching the intr_mode_init causes unexpected results on the system.
>>>>
>>>> Bypass it in enlighten_pv system.
>>>
>>> So that's the wrong patch order then. You broke XEN at some point with your
>>> changes. You need to prevent that breakage upfront not after the fact.
>>
>> Yes, I have considered to prevent that breakage in the patchset.
>>
>> Actually, Until the 11th patch, we put the intr_mode_init ahead of
>> time, which will break XEN.
>>
>> Before the 11th patch, we just unify the code and do the preparation,
>> Kernel will do the intr_mode_init like before, which will have no
>> influence on XEN.
>>
>> So we put the patch here before 11th patch.
>
> Ok. That's good, but please explain it in the changelog. I had the
> impression that this is fixing breakage you introduced earlier, but now
> with your explanation it makes sense. So the patch order is correct.
>
> Something like this wants to be in the changelog:
>
>   XEN PV overrides smp_prepare_cpus(). xen_pv_smp_prepare_cpus()
>   initializes interrupts in the XEN PV specific way and does not invoke
>   native_smp_prepare_cpus(). As a consequence, x86_init.intr_mode_init() is
>   not invoked either.
>
>   The invocation of x86_init.intr_mode_init() will be moved from
>   native_smp_prepare_cpus() in a follow up patch to solve <INSERT
>   REASON/PROBLEM>.
>
>   That move would cause the invocation of x86_init.intr_mode_init() for XEN
>   PV platforms. To prevent that, override the default x86_init.intr_mode_init()
>   callback with a noop().

Thank you very much for writing the changelog again.  This is really the 
true purpose which I couldn't explain clearly.

I am testing my V6 patchset, will send it out soon.

Thanks,

	dou.
>
> Thanks,
>
> 	tglx
>
>
>