Re: [PATCH v2 2/4] mm: x86: Invoke hypercall when page encryption status is changed

[Paolo Bonzini]

On 14/05/21 11:05, Ashish Kalra wrote:
> I absolutely agree with both of your point of view. But what's the
> alternative ?
>
> Ideally we should fail/stop migration even if a single guest page
> encryption status cannot be notified and that should be the way to
> proceed in this case, the guest kernel should notify the source
> userspace VMM to block/stop migration in this case.
>
>  From a practical side, i do see Qemu's migrate_add_blocker() interface
> but that looks to be a static interface and also i don't think it will
> force stop an ongoing migration, is there an existing mechanism
> to inform userspace VMM from kernel about blocking/stopping migration ?

On the Linux side, all you need to do is WARN and write 0 to the 
MIGRATION_CONTROL MSR.

QEMU can check the MSR value when migrating the CPU registers at the 
end, and fail migration if the MSR value is 0.

Paolo