Re: [Xen-devel] [PATCH v5 10/12] x86/xen: Bypass intr mode setup in enlighten_pv system

[Dou Liyang <douly.fnst@xxxxxxxxxxxxxx>]

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


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