linux-kernel - RE: [PATCH 1/1] x86/hyper-V: Allocate the IDT entry early in boot

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Date:   Wed, 13 Sep 2017 18:05:04 +0000
From:   KY Srinivasan <kys@...rosoft.com>
To:     Ingo Molnar <mingo@...nel.org>
CC:     Dan Carpenter <dan.carpenter@...cle.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
        "olaf@...fle.de" <olaf@...fle.de>,
        "apw@...onical.com" <apw@...onical.com>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "hpa@...or.com" <hpa@...or.com>
Subject: RE: [PATCH 1/1] x86/hyper-V: Allocate the IDT entry early in boot



> -----Original Message-----
> From: Ingo Molnar [mailto:mingo.kernel.org@...il.com] On Behalf Of Ingo
> Molnar
> Sent: Wednesday, September 13, 2017 2:01 AM
> To: KY Srinivasan <kys@...rosoft.com>
> Cc: Dan Carpenter <dan.carpenter@...cle.com>; x86@...nel.org;
> gregkh@...uxfoundation.org; linux-kernel@...r.kernel.org;
> devel@...uxdriverproject.org; olaf@...fle.de; apw@...onical.com;
> jasowang@...hat.com; tglx@...utronix.de; hpa@...or.com
> Subject: Re: [PATCH 1/1] x86/hyper-V: Allocate the IDT entry early in boot
> 
> 
> * KY Srinivasan <kys@...rosoft.com> wrote:
> 
> >
> >
> > > -----Original Message-----
> > > From: Dan Carpenter [mailto:dan.carpenter@...cle.com]
> > > Sent: Saturday, September 9, 2017 4:04 AM
> > > To: KY Srinivasan <kys@...rosoft.com>
> > > Cc: x86@...nel.org; gregkh@...uxfoundation.org; linux-
> > > kernel@...r.kernel.org; devel@...uxdriverproject.org; olaf@...fle.de;
> > > apw@...onical.com; jasowang@...hat.com; tglx@...utronix.de;
> > > hpa@...or.com; mingo@...nel.org
> > > Subject: Re: [PATCH 1/1] x86/hyper-V: Allocate the IDT entry early in boot
> > >
> > > On Fri, Sep 08, 2017 at 04:15:57PM -0700, kys@...hange.microsoft.com
> > > wrote:
> > > > From: "K. Y. Srinivasan" <kys@...rosoft.com>
> > > >
> > > > Allocate the hypervisor callback IDT entry early in the boot sequence.
> > > >
> > >
> > > I'm guessing this fixes a NULL dereference or something?  The changelog
> > > doesn't really say why we are doing this.
> >
> > The changelog does say what we are doing - allocating the IDT entry early in
> the boot sequence.
> 
> But the question was the 'why', not the 'what' - so Dan's question is
> fully justified ...
> 
> > The current code would allocate the entry as part of registering the handler
> > when vmbus driver loaded and this caused a problem for the cleanup
> Thomas had
> > implemented.
> 
> I've put this explanation into the changelog.

You are right. Thanks, Ingo.

K. Y
> 
> Thanks,
> 
> 	Ingo