Peter Maydell <peter.maydell@xxxxxxxxxx> writes: > On Wed, 21 Nov 2018 at 14:34, gengdongjiu <gengdongjiu@xxxxxxxxxx> wrote: >> >> 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. -- Alex Bennée
