From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Raj, Ashok" <ashok.raj@intel.com>
Subject: Re: [Qemu-devel] [Patch V2 1/2] x86, mce: Basic support to add LMCE
 support to QEMU
Date: Mon, 14 Dec 2015 14:05:33 -0500
Message-ID: <20151214190533.GA18012@otc-brkl-03.jf.intel.com>
References: <1449776482-26070-1-git-send-email-ashok.raj@intel.com>
 <20151214162356.GA5314@thinpad.lan.raisama.net>
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Cc: kvm@vger.kernel.org, Tony Luck <tony.luck@intel.com>,
	Gong Chen <gong.chen@intel.com>,
	Gleb Natapov <gleb@kernel.org>, linux-kernel@vger.kernel.org,
	qemu-devel@nongnu.org, Andi Kleen <andi.kleen@intel.com>,
	Paolo Bonzini <pbonzini@redhat.com>, Boris Petkov <bp@suse.de>,
	Ashok Raj <ashok.raj@intel.com>
To: Eduardo Habkost <ehabkost@redhat.com>
Return-path: <linux-kernel-owner@vger.kernel.org>
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In-Reply-To: <20151214162356.GA5314@thinpad.lan.raisama.net>
Sender: linux-kernel-owner@vger.kernel.org
List-Id: kvm.vger.kernel.org

Hi Eduardo,

Thanks for the feedback. All the suggestions make sense..

On Mon, Dec 14, 2015 at 02:23:56PM -0200, Eduardo Habkost wrote:
> > +static void feature_control_init(X86CPU *cpu)
> > +{
> > +	CPUX86State *cenv = &cpu->env;
> > +
> > +	cenv->msr_ia32_feature_control = ((1<<20) | (1<<0));
> 
> FEATURE_CONTROL_LOCKED and FEATURE_CONTROL_LMCE macros would make
> the code clearer.

Makes sense.. will fix it next round.

> > @@ -282,8 +282,9 @@
> >  
> >  #define MCG_CTL_P       (1ULL<<8)   /* MCG_CAP register available */
> >  #define MCG_SER_P       (1ULL<<24) /* MCA recovery/new status bits */
> > +#define MCG_LMCE_P	(1ULL<<27) /* Local Machine Check Supported */
> 
> Please use spaces instead of tabs. You can detect this and other
> coding style issues in this patch with checkpatch.pl.
> 

Will change the ones i added. 

> 
> >  
> > -#define MCE_CAP_DEF     (MCG_CTL_P|MCG_SER_P)
> > +#define MCE_CAP_DEF     (MCG_CTL_P|MCG_SER_P|MCG_LMCE_P)
> 
> This makes mcg_cap change when upgrading QEMU.
> 
> VMs with MCG_LMCE_P enabled shouldn't be migratable to hosts
> running older kernels, or the guest may try to read or write
> MSR_IA32_MCG_EXT_CTL after miration and get a #GP. That means:
> 
> 1) Older machine-types (pc-2.5 and older) should keep the
>    old (MCG_CTL_P|MCG_SER_P) default.
> 2) We can't make pc-2.6 enable LMCE by default, either, because
>    QEMU guarantees that just changing the machine-type shouldn't
>    introduce new host requirements (see:
>    http://article.gmane.org/gmane.comp.emulators.qemu/346651)
> 
> It looks like we need a new -cpu option to enable the feature,
> then. At least until we raise the minimum kernel version
> requirements of QEMU.

Ok.. i will look this up. 
> 
> (I didn't review the kvm_mce_inject() changes as I am not
> familiar with the details of how LMCE is implemented.)
> 
This is quite simple.. we just don't broadcast MCE's and set LMCE in 
MCG_STATUS.

I will make the suggested changes and resend.

Cheers,
Ashok