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

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Date:   Fri, 8 Sep 2017 19:09:18 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
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?

Thanks,

	tglx