On Thu, 2017-11-16 at 10:50 +0800, Quan Xu wrote: > > On 2017-11-15 22:43, Rik van Riel wrote: > > Can you explain why you believe that? > > for example, a vcpu thread is running in kvm mode under cretical > condition to stop. QEMU send an IPI to cause a VM-exit to happen > immediately, and this IPI doesn't make vcpu return to QEMU. IIUC > this vcpu thread will still continue to run in kvm mode when is > waked up at targer machine. with your patch, I don't see a chance > to load guest FPU or XSTATE, until return to QEMU and run kvm mode > again. > > then the FPU or XSTATE status is inconsistent for a small window, > what's > even > worse is that the vcpu is running. > > Did I misunderstand? At context switch time, the context switch code will save the guest FPU state to current->thread.fpu when the VCPU thread is scheduled out. When the VCPU thread is scheduled back in, the context switch code will restore current->thread.fpu to the FPU registers. The VCPU thread will never run with anything else than the guest FPU state, while inside the KVM_RUN code.
