> >> > >> Hi Peter, > >> Thanks for the review and comments. > >> > >> > > >> > On 8 November 2018 at 10:29, Dongjiu Geng <gengdongjiu@xxxxxxxxxx> wrote: > >> > > +bool write_part_cpustate_to_list(ARMCPU *cpu, ptrdiff_t > >> > > +fieldoffset) > >> > > >> > What is this about? Nothing else in QEMU needs to mess with the > >> > cpustate synchronization. My first assumption is that you should not need to do so either. > >> > >> We should change the guest CP15 ESR_EL1's value, the only method is > >> to change the cpu->cpreg_values[] in QEMU, then QEMU call write_list_to_kvmstate() to set the cpu->cpreg_values[] to KVM which > include the specified ESR_EL1 value, KVM do world switch, and then set the specified ESR_EL1's value to guest kernel. > > > > Ah, I see. This is a bug in our current handling of the register > > state, where we implicitly assume that nothing in QEMU will ever want > > to change any system register values. This assumption is now false -- > > kvm_arm_handle_debug() broke it -- so we need to fix the code that > > does kvm_arch_put_registers(). There is a comment in the kvm32.c > > version of that function about this. (The kvm64.c version has the same > > assumption but doesn't comment on it.) > > > > We should (ideally) fix this bug in the code that does register > > syncing, without requiring places in QEMU that update system registers > > to have to manually indicate which registers they have changed. I'll > > have a think about how best to do this. > > > >> About the detailed explanation, as shown in [2]. > >> > >> kvm_arm_handle_debug() does not need to do this because QEMU does not need to change CP15 registers, such as ESR_EL1. > > > > kvm_arm_handle_debug does change ESR_EL1: it is injecting an exception > > and so should set the exception register. This happens when it calls > > the do_interrupt() hook, because arm_cpu_do_interrupt_aarch64() writes > > to env->cp15.esr_el[new_el]. > > > > I'm not entirely sure why this is working today, in fact. > > Alex, did you test whether our debug-exception-injection reports the > > correct ESR_EL1 to the guest ? > <snip> > > I did not - I was mostly focusing in the host-debugging-the-guest test case. I'll get a test rig up and check. Thanks, please test it in the KVM mode, not in the TCG mode. Waiting for your test result. > > -- > Alex Bennée
