Subject: Re: [PATCH v3 1/2] KVM: PPC: New capability to control MCE behaviour

From: David Gibson <[email-masked]>
Date: Thu, 14 Jan 2016 11:02:39 +1100

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.
> 
> QEMU part can be found at:
> http://lists.nongnu.org/archive/html/qemu-ppc/2015-12/msg00199.html
> 
> Change Log v3:
>   - Split the patch into 2. First patch introduces the
>     new capability while the second one enhances KVM to
>     redirect MCE.
>   - Fix access width bug
>   - Rebased to v4.4-rc7
> 
> Change Log v2:
>   - Added KVM capability
> 
> Signed-off-by: Aravinda Prasad <[email-masked]>
> ---
>  arch/powerpc/include/asm/kvm_host.h |    1 +
>  arch/powerpc/kernel/asm-offsets.c   |    1 +
>  arch/powerpc/kvm/powerpc.c          |    7 +++++++
>  include/uapi/linux/kvm.h            |    1 +
>  4 files changed, 10 insertions(+)
> 
> diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
> index cfa758c..9ac2b84 100644
> --- a/arch/powerpc/include/asm/kvm_host.h
> +++ b/arch/powerpc/include/asm/kvm_host.h
> @@ -243,6 +243,7 @@ struct kvm_arch {
>  	int hpt_cma_alloc;
>  	struct dentry *debugfs_dir;
>  	struct dentry *htab_dentry;
> +	u8 fwnmi_enabled;

Um.. I don't see anything in this patch or 2/2 which actually tests
this flag...

>  #endif /* CONFIG_KVM_BOOK3S_HV_POSSIBLE */
>  #ifdef CONFIG_KVM_BOOK3S_PR_POSSIBLE
>  	struct mutex hpt_mutex;
> diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
> index 221d584..6a4e81a 100644
> --- a/arch/powerpc/kernel/asm-offsets.c
> +++ b/arch/powerpc/kernel/asm-offsets.c
> @@ -506,6 +506,7 @@ int main(void)
>  	DEFINE(KVM_ENABLED_HCALLS, offsetof(struct kvm, arch.enabled_hcalls));
>  	DEFINE(KVM_LPCR, offsetof(struct kvm, arch.lpcr));
>  	DEFINE(KVM_VRMA_SLB_V, offsetof(struct kvm, arch.vrma_slb_v));
> +	DEFINE(KVM_FWNMI, offsetof(struct kvm, arch.fwnmi_enabled));
>  	DEFINE(VCPU_DSISR, offsetof(struct kvm_vcpu, arch.shregs.dsisr));
>  	DEFINE(VCPU_DAR, offsetof(struct kvm_vcpu, arch.shregs.dar));
>  	DEFINE(VCPU_VPA, offsetof(struct kvm_vcpu, arch.vpa.pinned_addr));
> diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
> index 6fd2405..a8399b5 100644
> --- a/arch/powerpc/kvm/powerpc.c
> +++ b/arch/powerpc/kvm/powerpc.c
> @@ -570,6 +570,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>  		r = 1;
>  		break;
>  #endif
> +	case KVM_CAP_PPC_FWNMI:
> +		r = 1;
> +		break;
>  	default:
>  		r = 0;
>  		break;
> @@ -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;
>  	default:
>  		r = -EINVAL;
>  		break;
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 03f3618..d8a07b5 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -831,6 +831,7 @@ struct kvm_ppc_smmu_info {
>  #define KVM_CAP_GUEST_DEBUG_HW_WPS 120
>  #define KVM_CAP_SPLIT_IRQCHIP 121
>  #define KVM_CAP_IOEVENTFD_ANY_LENGTH 122
> +#define KVM_CAP_PPC_FWNMI 123
>  
>  #ifdef KVM_CAP_IRQ_ROUTING
>  
> 

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
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