linux-kernel - Re: [Qemu-devel] [Patch V2 1/2] x86, mce: Basic support to add LMCE support to QEMU

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Date:	Mon, 14 Dec 2015 19:17:27 -0500
From:	"Raj, Ashok" <ashok.raj@...el.com>
To:	Borislav Petkov <bp@...e.de>
Cc:	Eduardo Habkost <ehabkost@...hat.com>, kvm@...r.kernel.org,
	Tony Luck <tony.luck@...el.com>,
	Gong Chen <gong.chen@...el.com>,
	Gleb Natapov <gleb@...nel.org>, linux-kernel@...r.kernel.org,
	qemu-devel@...gnu.org, Andi Kleen <andi.kleen@...el.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Ashok Raj <ashok.raj@...el.com>
Subject: Re: [Qemu-devel] [Patch V2 1/2] x86, mce: Basic support to add LMCE
 support to QEMU

On Mon, Dec 14, 2015 at 11:37:16PM +0100, Borislav Petkov wrote:
> On Mon, Dec 14, 2015 at 02:11:46PM -0500, Raj, Ashok wrote:
> > This is mostly harmless.. since the MCG_CAP space is shared and has no
> > conflict between vendors. Also just the CAP being set has no effect.
> 
> Of course it does - we check SER_P in machine_check_poll() and when
> I emulate an AMD guest and inject errors into it, error handling is
> obviously wrong, see:
> 
> https://lkml.kernel.org/r/20151123150355.GE5134@pd.tnic
> 

I can see how this hurts.. since the poller isn't doing cpu model specific 
stuff..?

in the LMCE case, even if you advertise MCG_LMCE_P in MCG_CAP, the guest kernel 
wont call intel_init_lmce() only from mce_intel.c.. so the same problem
won't happen.

but the issue Eduardo mentioned seems like the following.

New QEMU_LMCE + New KVM_LMCE + New_GUEST_LMCE - No problem

but if you were to migrage the Guest_LMCE to a non-LMCE supported KVM host
we could run into an issue.. 

is this the compatibility issue that you were looking to fix Eduardo?

Cheers,
Ashok
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