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 11:00:56 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     KY Srinivasan <kys@...rosoft.com>
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


* 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.

Thanks,

	Ingo