From mboxrd@z Thu Jan  1 00:00:00 1970
From: Borislav Petkov <bp@suse.de>
Subject: Re: [Qemu-devel] [Patch V2 1/2] x86, mce: Basic support to add LMCE
 support to QEMU
Date: Mon, 14 Dec 2015 17:37:38 +0100
Message-ID: <20151214163738.GJ11630@pd.tnic>
References: <1449776482-26070-1-git-send-email-ashok.raj@intel.com>
 <20151214162356.GA5314@thinpad.lan.raisama.net>
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Cc: Ashok Raj <ashok.raj@intel.com>, 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>
To: Eduardo Habkost <ehabkost@redhat.com>
Return-path: <linux-kernel-owner@vger.kernel.org>
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Sender: linux-kernel-owner@vger.kernel.org
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On Mon, Dec 14, 2015 at 02:23:56PM -0200, Eduardo Habkost wrote:
> > -#define MCE_CAP_DEF     (MCG_CTL_P|MCG_SER_P)
> > +#define MCE_CAP_DEF     (MCG_CTL_P|MCG_SER_P|MCG_LMCE_P)
>=20
> This makes mcg_cap change when upgrading QEMU.
>=20
> 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:
>=20
> 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)
>=20
> 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.

=2E.. and obviously LMCE is vendor-specific so it cannot be enabled on
!Intel guests with a define like that. mce_init() in qemu should check
vendor too.

The same mistake was done with SER_P but that's much harder to change,
as we discussed previously.

--=20
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imend=C3=B6rffer, Jane Smithard, Graham Nort=
on, HRB 21284 (AG N=C3=BCrnberg)
--=20