linux-kernel - RE: [PATCH] x86/hyper-v: Zero out the VP assist page to fix CPU offlining

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Message-ID: <PU1P153MB01690BCF3771C221C3677158BFC80@PU1P153MB0169.APCP153.PROD.OUTLOOK.COM>
Date:   Thu, 18 Jul 2019 08:04:38 +0000
From:   Dexuan Cui <decui@...rosoft.com>
To:     Thomas Gleixner <tglx@...utronix.de>
CC:     Haiyang Zhang <haiyangz@...rosoft.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Sasha Levin <Alexander.Levin@...rosoft.com>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        Long Li <longli@...rosoft.com>, vkuznets <vkuznets@...hat.com>,
        Ingo Molnar <mingo@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "marcelo.cerri@...onical.com" <marcelo.cerri@...onical.com>,
        "driverdev-devel@...uxdriverproject.org" 
        <driverdev-devel@...uxdriverproject.org>,
        "olaf@...fle.de" <olaf@...fle.de>,
        "apw@...onical.com" <apw@...onical.com>,
        "jasowang@...hat.com" <jasowang@...hat.com>
Subject: RE: [PATCH] x86/hyper-v: Zero out the VP assist page to fix CPU
 offlining

> From: Thomas Gleixner <tglx@...utronix.de>
> Sent: Thursday, July 18, 2019 12:56 AM
> To: Dexuan Cui <decui@...rosoft.com>
> 
> On Thu, 18 Jul 2019, Dexuan Cui wrote:
> >
> > The concept of the "overlay page" seems weird, and frankly speaking,
> > I don't really understand why the Hyper-V guys invented it, but as far
> > as this patch here is concerned, I think the patch is safe and it can
> > indeed fix the CPU offlining issue I described.
> 
> Then this needs some really good explanation and in the change log because
> that's really obscure behaviour.
> 
> 	tglx

Agreed. I'll combine my replies into the changelog and post a v2 of
the one-line patch.

Thanks,
-- Dexuan