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. Alex _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/cucslists/listinfo/kvmarm
