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? :)
>
>>> 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.
MOL uses OSI calls instead of MMIO. So yes, it is heavily used.
Alex--
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