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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