Re: [PATCH] KVM: x86: Add instruction length to VCPU event state

[Gleb Natapov <gleb@redhat.com>]

On Sat, Feb 13, 2010 at 10:51:40AM +0100, Jan Kiszka wrote:
> From: Jan Kiszka <jan.kiszka@siemens.com>
> 
> VMX requires a properly set instruction length VM entry field when
> trying to inject soft exception and interrupts. We have to preserve this
> state across VM save/restore to avoid breaking the re-injection of such
> events on Intel. So add it to the new VCPU event state.
> 
We shouldn't re-inject soft exceptions/interrupts after migration, but
re-execute instruction instead. Instruction length field doesn't exist
on SVM and migration shouldn't expose implementation details.

> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> ---
> 
> Existing qemu[-kvm]-0.12 that is already prepared for 2.6.33 will need
> an update now. Whenever we actually ran into the case that
> event_exit_inst_len was evaluated by VMX, we were playing roulette with
> a high probability to crash the guest. This will not changes for already
> released 0.12.x versions.
> 
>  Documentation/kvm/api.txt  |    2 ++
>  arch/x86/include/asm/kvm.h |    3 ++-
>  arch/x86/kvm/x86.c         |    4 ++++
>  3 files changed, 8 insertions(+), 1 deletions(-)
> 
> diff --git a/Documentation/kvm/api.txt b/Documentation/kvm/api.txt
> index c6416a3..aa11d70 100644
> --- a/Documentation/kvm/api.txt
> +++ b/Documentation/kvm/api.txt
> @@ -686,6 +686,8 @@ struct kvm_vcpu_events {
>  	} nmi;
>  	__u32 sipi_vector;
>  	__u32 flags;
> +	__u32 instruction_length; /* used by VMX */
> +	__u32 reserved[9];
>  };
>  
>  4.30 KVM_SET_VCPU_EVENTS
> diff --git a/arch/x86/include/asm/kvm.h b/arch/x86/include/asm/kvm.h
> index f46b79f..570b6cc 100644
> --- a/arch/x86/include/asm/kvm.h
> +++ b/arch/x86/include/asm/kvm.h
> @@ -281,7 +281,8 @@ struct kvm_vcpu_events {
>  	} nmi;
>  	__u32 sipi_vector;
>  	__u32 flags;
> -	__u32 reserved[10];
> +	__u32 instruction_length; /* used by VMX */
> +	__u32 reserved[9];
>  };
>  
>  #endif /* _ASM_X86_KVM_H */
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 86b739f..0cc6cfb 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -2134,6 +2134,8 @@ static void kvm_vcpu_ioctl_x86_get_vcpu_events(struct kvm_vcpu *vcpu,
>  	events->nmi.pending = vcpu->arch.nmi_pending;
>  	events->nmi.masked = kvm_x86_ops->get_nmi_mask(vcpu);
>  
> +	events->instruction_length = vcpu->arch.event_exit_inst_len;
> +
>  	events->sipi_vector = vcpu->arch.sipi_vector;
>  
>  	events->flags = (KVM_VCPUEVENT_VALID_NMI_PENDING
> @@ -2170,6 +2172,8 @@ static int kvm_vcpu_ioctl_x86_set_vcpu_events(struct kvm_vcpu *vcpu,
>  	if (events->flags & KVM_VCPUEVENT_VALID_SIPI_VECTOR)
>  		vcpu->arch.sipi_vector = events->sipi_vector;
>  
> +	vcpu->arch.event_exit_inst_len = events->instruction_length;
> +
>  	vcpu_put(vcpu);
>  
>  	return 0;
> 



--
			Gleb.