[PATCH v2] ARM/KVM: save and restore generic timer registers
Christoffer Dall
christoffer.dall at linaro.org
Thu Jun 20 16:37:15 EDT 2013
On Thu, Jun 20, 2013 at 08:29:30PM +0100, Peter Maydell wrote:
> On 20 June 2013 19:32, Christoffer Dall <christoffer.dall at linaro.org> wrote:
> > Marc wrote:
> >> So there is just one thing we absolutely need to make sure here: no vcpu
> >> can run before they've all had their timer restored, and hence a stable
> >> cntvoff. Otherwise two vcpus will have a different view of time.
> >>
> >> Can we guarantee this?
>
> > Do we need to? User space is free to modify time and all sort of other
> > registers at any point during VM execution - it will just break the
> > guest that it's running.
>
> Note that QEMU will stop all CPUs before doing a migration or
> similar operation. However there is a monitor command to query
> the current CPU registers etc which won't try to stop the VM
> first. So we might try to read vcpu registers (though I hope we
> don't allow writing them).
>
Sounds like we need to add a -EBUSY return on SET_ONE_REG if the VM is
running.
-Christoffer
More information about the linux-arm-kernel
mailing list