On Sat, Oct 27, 2012 at 11:52 AM, Peter Maydell <peter.maydell@xxxxxxxxxx> wrote: > On 27 October 2012 04:00, haibin wang <wanghaibin202@xxxxxxxxx> wrote: >> There is a doubt about qemu ! >> >> At present, when the host kernel (kvm) didn't configure CONFIG_KVM_ARM_VGIC, >> qemu load guest kernel(without CONFIG_ARCH_TIMER configuration) will be failure, >> and print: >> "KVM Cortex-A15 without in-kernel VGIC is not a >> valid configuration. Check that: >> * you have passed -machine kernel_irqchip=on to QEMU >> * your host kernel was built with CONFIG_KVM_ARM_VGIC >> * the device tree passed to your host kernel has a " >> valid node for the GIC" >> >> In my opinion, loading guest kernel using GIC by qemu's simulating >> must be successful . (I remeber that the host kernel of brach v5 >> didn't simulate VGIC in kvm. At that >> time, we loaded the guest kernel using GIC which qemu simulated). > > We've discussed this before. The problem is that it's not possible > for emulation of the architected cp15 timer to be done in userspace > [there is no way to trap the cp15 accesses so they can be forwarded > to userspace]. And an in-kernel cp15 timer implementation requires > an in-kernel GIC implementation. So it seemed easier to insist > on this configuration (which is what everybody will be running anyway > for performance reasons) rather than try to support an odd config > that doesn't make much sense. > > As it happens, the current RFC set of QEMU patches don't insist > on the in-kernel irqchip, because I wanted them to at least > vaguely work (for guests that don't touch the cp15 timers) with > Christoffer's base-level kernel patches that we're trying to upstream. > But when the VGIC support goes upstream I'll probably reintroduce this > check and error message into the QEMU side. > FYI the current patch series upstream effort includes the VGIC patches, but I don't think anyone ever measured the performance benefit of the VGIC yet. -Christoffer _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/cucslists/listinfo/kvmarm
