Re: [PATCH 13/15] Add NMI injection support to SVM.

[Gleb Natapov <gleb@redhat.com>]

On Sun, Apr 19, 2009 at 04:21:29PM +0300, Avi Kivity wrote:
> Gleb Natapov wrote:
>> On Fri, Apr 17, 2009 at 09:55:45PM +0200, Jan Kiszka wrote:
>>   
>>> Gleb Natapov wrote:
>>>     
>>>> Signed-off-by: Gleb Natapov <gleb@redhat.com>
>>>> ---
>>>>  arch/x86/include/asm/kvm_host.h |    1 +
>>>>  arch/x86/kvm/svm.c              |   49 +++++++++++++++++++++++++++++++++++++-
>>>>  2 files changed, 48 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
>>>> index 8b6f6e9..057a612 100644
>>>> --- a/arch/x86/include/asm/kvm_host.h
>>>> +++ b/arch/x86/include/asm/kvm_host.h
>>>> @@ -766,6 +766,7 @@ enum {
>>>>  #define HF_GIF_MASK		(1 << 0)
>>>>  #define HF_HIF_MASK		(1 << 1)
>>>>  #define HF_VINTR_MASK		(1 << 2)
>>>> +#define HF_NMI_MASK		(1 << 3)
>>>>   /*
>>>>   * Hardware virtualization extension instructions may fault if a
>>>> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
>>>> index c605477..cd60fd7 100644
>>>> --- a/arch/x86/kvm/svm.c
>>>> +++ b/arch/x86/kvm/svm.c
>>>> @@ -1834,6 +1834,13 @@ static int cpuid_interception(struct vcpu_svm *svm, struct kvm_run *kvm_run)
>>>>  	return 1;
>>>>  }
>>>>  +static int iret_interception(struct vcpu_svm *svm, struct kvm_run 
>>>> *kvm_run)
>>>> +{
>>>> +	svm->vmcb->control.intercept &= ~(1UL << INTERCEPT_IRET);
>>>> +	svm->vcpu.arch.hflags &= ~HF_NMI_MASK;
>>>> +	return 0;
>>>> +}
>>>>       
>>> First, this must return 1 (or set an exit reason, but there is no reason
>>> to escape to user space here). And second, I think a corner case is not
>>> handled the same way as on real iron: If there is already the next NMI
>>> waiting, we will inject it before iret, not after its execution as it
>>> should be.
>>>
>>> No easy solution for this yet. Maybe emulating iret, but there is no
>>> implementation, specifically for protected mode. Maybe setting a
>>> breakpoint. Or maybe enforcing a single step exception. Nothing trivial
>>> in this list. On the other hand, this may only be a slight imprecision
>>> of the virtualization. Need to think about it.
>>>
>>>     
>> What about this:
>> Instead of clearing HF_NMI_MASK in iret_interception() we can set
>> another flag (HF_IRET) and on guest entry clear HF_NMI_MASK (and
>> HF_IRET) if HF_IRET is set, but do that after checking for NMI
>> injection. The pending NMI will be injected on the next entry.
>> Also not how real HW works, but may be better then current situation.
>>   
>
> There may not be a next entry if the guest is in a tight loop.  Given  
> NMIs are used for watchdogs, that's not good.
>
We don't exit a guest after kvm time slice ends?

--
			Gleb.