linux-kernel - RE: [PATCH] x86/idt: Unbreak MS HyperV hypercall vector install

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Message-ID: <DM5PR21MB047621863EBCACCA1AF81A1AA0950@DM5PR21MB0476.namprd21.prod.outlook.com>
Date:   Fri, 8 Sep 2017 17:15:22 +0000
From:   KY Srinivasan <kys@...rosoft.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Stephen Hemminger <stephen@...workplumber.org>
CC:     LKML <linux-kernel@...r.kernel.org>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Simon Xiao <sixiao@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        "Peter Zijlstra" <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        "Brian Gerst" <brgerst@...il.com>, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>
Subject: RE: [PATCH] x86/idt: Unbreak MS HyperV hypercall vector install



> -----Original Message-----
> From: Thomas Gleixner [mailto:tglx@...utronix.de]
> Sent: Friday, September 8, 2017 10:09 AM
> To: Stephen Hemminger <stephen@...workplumber.org>
> Cc: LKML <linux-kernel@...r.kernel.org>; Stephen Hemminger
> <sthemmin@...rosoft.com>; Simon Xiao <sixiao@...rosoft.com>; KY
> Srinivasan <kys@...rosoft.com>; Haiyang Zhang
> <haiyangz@...rosoft.com>; Steven Rostedt <rostedt@...dmis.org>; Peter
> Zijlstra <peterz@...radead.org>; Linus Torvalds <torvalds@...ux-
> foundation.org>; Josh Poimboeuf <jpoimboe@...hat.com>; H. Peter Anvin
> <hpa@...or.com>; Denys Vlasenko <dvlasenk@...hat.com>; Brian Gerst
> <brgerst@...il.com>; Borislav Petkov <bp@...en8.de>; Andy Lutomirski
> <luto@...nel.org>
> Subject: Re: [PATCH] x86/idt: Unbreak MS HyperV hypercall vector install
> 
> On Fri, 8 Sep 2017, Stephen Hemminger wrote:
> > On Fri, 8 Sep 2017 01:19:52 -0700
> > "Thomas Gleixner" <tglx@...utronix.de> wrote:
> >
> > > The rework of the IDT setup changed the way how unused system gates
> are
> > > accounted. At the end of the gate initialization all unused gates in the
> > > system vector area are set to the spurios handler and marked as used for
> > > consistency reasons.
> > >
> > > Marking them as used breaks MS HyperV because it installs its hypercall
> > > vector after that point and the installation is guarded by the bit in the
> > > used_vectors map. So the hyperv vector stays directed to the spurious
> > > interrupt handler.
> > >
> > > Leave them marked as unused again and unbreak HyperV that way.
> > >
> > > Fixes: dc20b2d52653 ("x86/idt: Move interrupt gate initialization to IDT
> > > code")
> > > Reported-by: Stephen Hemminger <sthemmin@...rosoft.com>
> > > Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> >
> > This fixes it, thanks.
> >
> > Tested-by: Stephen Hemminger <sthemmin@...rosoft.com>
> 
> What's the reason that the vector is not set up early in the boot process?

No specific reason other than that was the way I had coded it up initially. I will send in a patch to
fix that.

Regards,

K. Y 
> 
> Thanks,
> 
> 	tglx
>