Re: [PATCH 1/1] Disable GUEST_INTR_STATE_STI flag before injecting NMI to guest on VMX

[Jan Kiszka <jan.kiszka@siemens.com>]

Am 26.08.2010 22:06, Jes.Sorensen@redhat.com wrote:
> From: Jes Sorensen <Jes.Sorensen@redhat.com>
> 
> Injecting an NMI while GUEST_INTR_STATE_STI is set may fail,
> which can cause an EXIT with invalid state, resulting in the
> guest dieing.

Very interesting. Reality obviously doesn't bother about the statement
of the vendor [1].

Just curious: is this limited to specific CPU models or actually a
generic issue?

> 
> Credit to Gleb for figuring out why it was failing and how to
> fix it.
> 
> Signed-off-by: Jes Sorensen <Jes.Sorensen@redhat.com>
> Signed-off-by: Gleb Natapov <gleb@redhat.com>
> ---
>  arch/x86/kvm/vmx.c |    2 ++
>  1 files changed, 2 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index cf56462..8e95371 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -2888,6 +2888,8 @@ static void vmx_inject_nmi(struct kvm_vcpu *vcpu)
>  		kvm_rip_write(vcpu, vmx->rmode.irq.rip - 1);
>  		return;
>  	}
> +	vmcs_write32(GUEST_INTERRUPTIBILITY_INFO,
> +			vmcs_read32(GUEST_INTERRUPTIBILITY_INFO) & ~GUEST_INTR_STATE_STI);
>  	vmcs_write32(VM_ENTRY_INTR_INFO_FIELD,
>  			INTR_TYPE_NMI_INTR | INTR_INFO_VALID_MASK | NMI_VECTOR);
>  }

Thinking about the implications: Independent of virtualization, this
means that no code code can in any way rely on the STI shadow if there
are NMIs present that could "consume" it. Because after return from
those NMIs, interrupts could then be injected on the instruction that
was originally under the shadow.

Jan

[1] http://thread.gmane.org/gmane.comp.emulators.kvm.devel/52144

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