linux-kernel - Re: [PATCH v2 1/4] x86/hyper-v: move synic/stimer control structures definitions to hyperv-tlfs.h

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Date:   Thu, 29 Nov 2018 20:22:10 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
cc:     Nadav Amit <nadav.amit@...il.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "Michael Kelley (EOSG)" <Michael.H.Kelley@...rosoft.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        Radim Krčmář <rkrcmar@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        Roman Kagan <rkagan@...tuozzo.com>
Subject: Re: [PATCH v2 1/4] x86/hyper-v: move synic/stimer control structures
 definitions to hyperv-tlfs.h

On Thu, 29 Nov 2018, Vitaly Kuznetsov wrote:
> Nadav Amit <nadav.amit@...il.com> writes:
> 
> >> On Nov 28, 2018, at 5:07 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
> >> 
> >> On Wed, 28 Nov 2018, Vitaly Kuznetsov wrote:
> >> 
> >>> Nadav Amit <nadav.amit@...il.com> writes:
> >>> 
> >>>> On a different note: how come all of the hyper-v structs are not marked
> >>>> with the “packed" attribute?
> >>> 
> >>> "packed" should not be needed with proper padding; I vaguely remember
> >>> someone (from x86@?) arguing _against_ "packed".
> >> 
> >> Packed needs to be used, when describing fixed format data structures in
> >> hardware or other ABIs, so the compiler cannot put alignment holes into
> >> them.
> >> 
> >> Using packed for generic data structures might result in suboptimal layouts
> >> and prevents layout randomization.
> >
> > Right, I forgot about the structs randomization. So at least for it, the
> > attribute should be needed.
> >
> 
> Not sure when randomization.s used but Hyper-V drivers will of course be
> utterly broken with it.
> 
> > To prevent conflicts, I think that this series should also add the
> > attribute in a first patch, which would be tagged for stable.
> 
> As the patchset doesn't add new definitions and as Paolo already queued
> it I'd go with a follow-up patch adding "packed" to all hyperv-tlfs.h
> structures. The question is how to avoid conflicts when Linus will be
> merging this. We can do:
> - Topic branch in kvm
> - Send the patch to x86, make topic branch and reabse kvm
> - Send the patch to kvm
> - ... ?
> 
> Paolo/Thomas, what would be your preference?

As Paolo already has it, just route it through his tree please.

Thanks,

	tglx