Re: [PATCH 14/15] KVM: PPC: Add OSI hypercall interface

[Avi Kivity <avi-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

On 03/09/2010 03:12 PM, Alexander Graf wrote:
> On 09.03.2010, at 14:11, Avi Kivity wrote:
>
>    
>> On 03/09/2010 03:04 PM, Alexander Graf wrote:
>>      
>>>        
>>>>> +		/* KVM_EXIT_OSI */
>>>>> +		struct {
>>>>> +			__u64 gprs[32];
>>>>> +		} osi;
>>>>> +
>>>>> +MOL uses a special hypercall interface it calls 'OSI'. To enable it, we catch
>>>>> +hypercalls and exit with this exit struct that contains all the guest gprs.
>>>>> +
>>>>> +If exit_reason is KVM_EXIT_OSI, then the vcpu has triggered such a hypercall.
>>>>> +Userspace can now handle the hypercall and when it's done modify the gprs as
>>>>> +necessary. Upon guest entry all guest GPRs will then be replaced by the values
>>>>> +in this struct.
>>>>> +
>>>>>
>>>>>
>>>>>            
>>>> That's migration unsafe.  There may not be next guest entry on this host.
>>>>
>>>>          
>>> It's as unsafe as MMIO then.
>>>
>>>
>>>        
>>  From api.txt:
>>
>>      
>>> NOTE: For KVM_EXIT_IO and KVM_EXIT_MMIO, the corresponding operations
>>> are complete (and guest state is consistent) only after userspace has
>>> re-entered the kernel with KVM_RUN.  The kernel side will first finish
>>> incomplete operations and then check for pending signals.  Userspace
>>> can re-enter the guest with an unmasked signal pending to complete
>>> pending operations.
>>>        
>>      
> Alright - so I add KVM_EXIT_OSI there and be good? :)
>    

Sure, just verify that the note holds for that case too.

>> But we need to be migration safe.  If the interface is not heavily used, let's not add complications.
>>      
> MOL uses OSI calls instead of MMIO. So yes, it is heavily used.
>
>    

Ok.

-- 
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