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

[Avi Kivity <avi@redhat.com>]

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.


>> Is using KVM_[GS]ET_REGS problematic for some reason?
>>      
> It's two additional ioctls for no good reason. We know the interface, so we can model towards it.
>    

But we need to be migration safe.  If the interface is not heavily used, 
let's not add complications.

-- 
error compiling committee.c: too many arguments to function