From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <paulus@ozlabs.org>
Received: from ozlabs.org (ozlabs.org [IPv6:2401:3900:2:1::2])
 (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits))
 (No client certificate requested)
 by lists.ozlabs.org (Postfix) with ESMTPS id 51C431A0B6B
 for <linuxppc-dev@lists.ozlabs.org>; Sat, 23 Jan 2016 21:28:57 +1100 (AEDT)
Date: Sat, 23 Jan 2016 21:20:13 +1100
From: Paul Mackerras <paulus@ozlabs.org>
To: Aravinda Prasad <aravinda@linux.vnet.ibm.com>
Cc: gleb@kernel.org, agraf@suse.de, kvm-ppc@vger.kernel.org,
 linuxppc-dev@ozlabs.org, pbonzini@redhat.com,
 mahesh@linux.vnet.ibm.com, david@gibson.dropbear.id.au,
 kvm@vger.kernel.org, mpe@ellerman.id.au
Subject: Re: [PATCH v3 1/2] KVM: PPC: New capability to control MCE behaviour
Message-ID: <20160123102013.GA11916@fergus.ozlabs.ibm.com>
References: <20160113070759.20248.86252.stgit@aravindap>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
In-Reply-To: <20160113070759.20248.86252.stgit@aravindap>
List-Id: Linux on PowerPC Developers Mail List <linuxppc-dev.lists.ozlabs.org>
List-Unsubscribe: <https://lists.ozlabs.org/options/linuxppc-dev>,
 <mailto:linuxppc-dev-request@lists.ozlabs.org?subject=unsubscribe>
List-Archive: <http://lists.ozlabs.org/pipermail/linuxppc-dev/>
List-Post: <mailto:linuxppc-dev@lists.ozlabs.org>
List-Help: <mailto:linuxppc-dev-request@lists.ozlabs.org?subject=help>
List-Subscribe: <https://lists.ozlabs.org/listinfo/linuxppc-dev>,
 <mailto:linuxppc-dev-request@lists.ozlabs.org?subject=subscribe>

On Wed, Jan 13, 2016 at 12:37:59PM +0530, Aravinda Prasad wrote:
> This patch introduces a new KVM capability to control
> how KVM behaves on machine check exception (MCE).
> Without this capability, KVM redirects machine check
> exceptions to guest's 0x200 vector if the address in
> error belongs to the guest. With this capability KVM
> causes a guest exit with NMI exit reason.
> 
> This is required to avoid problems if a new kernel/KVM
> is used with an old QEMU for guests that don't issue
> "ibm,nmi-register". As old QEMU does not understand the
> NMI exit type, it treats it as a fatal error. However,
> the guest could have handled the machine check error
> if the exception was delivered to guest's 0x200 interrupt
> vector instead of NMI exit in case of old QEMU.

[snip]

> @@ -1132,6 +1135,10 @@ static int kvm_vcpu_ioctl_enable_cap(struct kvm_vcpu *vcpu,
>  		break;
>  	}
>  #endif /* CONFIG_KVM_XICS */
> +	case KVM_CAP_PPC_FWNMI:
> +		r = 0;
> +		vcpu->kvm->arch.fwnmi_enabled = true;
> +		break;

Might we ever want to set this flag back to false after setting it to
true?  If so perhaps we should do vcpu->kvm->arch.fwnmi_enabled =
!!cap->args[0].  However, I admit I can't actually think of a
situation where we would need to reset it. :)

Paul.