On Fri, 24 Feb 2023 18:36:23 +0000, Oliver Upton <oliver.upton@xxxxxxxxx> wrote: > > Hi Joey, > > On Fri, Feb 24, 2023 at 05:39:15PM +0000, Joey Gouly wrote: > > I'm having an issue with this commit where a VCPU is getting a CNTVOFF_EL2 set > > to 0, so it sees the same time as the host system, and the other VCPU has the > > correct offset. > > Yikes! > > > The flow of execution looks like this: > > KVM_CREATE_VCPU 0 (VMM) -> > > kvm_timer_vcpu_init -> > > update_vtimer_cntvoff (VCPU0.CNTVOFF_EL2=kvm_phys_timer_read) > > KVM_ARM_VCPU_INIT (VMM) -> > > kvm_arch_vcpu_ioctl_vcpu_init -> > > kvm_vcpu_set_target -> > > kvm_reset_vcpu -> > > kvm_reset_sys_regs (VCPU0.CNTVOFF_EL2=0) > > > > KVM_CREATE_VCPU 1 (VMM) -> > > kvm_timer_vcpu_init -> > > update_vtimer_cntvoff (VCPU0.CNTVOFF_EL2=VCPU1.CNTVOFF_EL2=kvm_phys_timer_read) > > KVM_ARM_VCPU_INIT (VMM) -> > > kvm_arch_vcpu_ioctl_vcpu_init -> > > kvm_vcpu_set_target -> > > kvm_reset_vcpu -> > > kvm_reset_sys_regs (VCPU1.CNTVOFF_EL2=0) > > > > At this point VCPU0 has CNTVOFF_EL2 == kvm_phys_timer_read, and VCPU1 > > has CNTVOFF_EL2 == 0. > > > > The VCPUs having different CNTVOFF_EL2 valuess is just a symptom of the fact that > > CNTVOFF_EL2 is now reset in kvm_reset_sys_regs. > > Right, and the fundamental problem at hand is that we used CNTVOFF_EL2 > to stash the _host's_ offset even though we are trying to change the > meaning of it to be part of the virtual EL2's context. What is driving me nuts is that I have never managed to reproduce the problem so far. I guess I have too much crap in my tree to spot it... > > > The following patch gets it booting again, but I'm sure it's not the right fix. > > I'd rather we just break the host away from using the shadow reg > altogether and separately track the host offset. As it so happens Marc > has a patch that does exactly that [*]. Yup, might as well fix that *and* kill the lock inversion issue in one go... > Marc, do you want to resend that patch in isolation addressing the > feedback and link to this bug report? > > [*] https://lore.kernel.org/kvmarm/20230216142123.2638675-6-maz@xxxxxxxxxx/ Joey, could you please give that patch a go, just to be on the safe side? Thanks, M. -- Without deviation from the norm, progress is not possible.
