Re: [Xen-devel] [PATCH] x86/hvm: Fix the unknown nested vmexit reason 80000021 bug

[George Dunlap <George.Dunlap@xxxxxxxxxxxxx>]

On Tue, Apr 7, 2015 at 5:11 PM, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
> On 07/04/15 14:27, Liang Li wrote:
>> This bug will be trigged when NMI happen in the L2 guest. The current
>> code handles the NMI incorrectly. According to Intel SDM 31.7.1.2
>> (Resuming Guest Software after Handling an Exception), If bit 31 of the
>> IDT-vectoring information fields is set, and the virtual NMIs VM-execution
>> control is 1, while bits 10:8 in the IDT-vectoring information field is
>> 2, bit 3 in the interruptibility-state field should be cleared to avoid
>> the next VM entry fail.
>>
>> Signed-off-by: Liang Li <liang.z.li@xxxxxxxxx>
>> ---
>>  xen/arch/x86/hvm/vmx/vmx.c | 6 +++---
>>  1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
>> index e1c55ce..b1f2df8 100644
>> --- a/xen/arch/x86/hvm/vmx/vmx.c
>> +++ b/xen/arch/x86/hvm/vmx/vmx.c
>> @@ -2621,7 +2621,8 @@ static void vmx_idtv_reinject(unsigned long idtv_info)
>>           * Clear NMI-blocking interruptibility info if an NMI delivery 
>> faulted.
>>           * Re-delivery will re-set it (see SDM 3B 25.7.1.2).
>>           */
>> -        if ( (idtv_info & INTR_INFO_INTR_TYPE_MASK) == 
>> (X86_EVENTTYPE_NMI<<8) )
>> +        if ( cpu_has_vmx_vnmi && ((idtv_info & INTR_INFO_INTR_TYPE_MASK) ==
>> +                                 (X86_EVENTTYPE_NMI<<8)) )
>
> This would be easier to read as
>
> if ( cpu_has_vmx_vnmi &&
>      (idtv_info & INTR_INFO_INTR_TYPE_MASK) == (X86_EVENTTYPE_NMI<<8)) )

I was going to say something similar, but I think in the past Jan has
said that Liang's original is more in line with the coding style.

But I'll let him comment.

 -George

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