On 20.06.2013, at 23:59, Peter Maydell wrote: > On 20 June 2013 22:55, Alexander Graf <agraf@xxxxxxx> wrote: >> >> On 20.06.2013, at 22:37, Christoffer Dall wrote: >> >>> On Thu, Jun 20, 2013 at 08:29:30PM +0100, Peter Maydell wrote: >>>> On 20 June 2013 19:32, Christoffer Dall <christoffer.dall@xxxxxxxxxx> 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. >> >> The ONE_REG API should already be protected here, as it does >> vcpu_load() in kvm_vcpu_ioctl(). So a separate thread can't possibly >> do ONE_REG accesses while another thread has the same vcpu running. > > Doesn't protect you against confusion due to another thread running > a different vcpu in the same vm, though. Ah, different ONE_REG API. Can't you just notify all vcpus to exit and refresh their timers? That's what kvm_make_request() is there for, no? Alex _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/cucslists/listinfo/kvmarm
