Julien Thierry <julien.thie...@arm.com> writes: > Hi Alex, > > On 09/11/17 17:00, Alex Bennée wrote: >> The system state of KVM when using userspace emulation is not complete >> until we return into KVM_RUN. To handle mmio related updates we wait >> until they have been committed and then schedule our KVM_EXIT_DEBUG. >> >> The kvm_arm_handle_step_debug() helper tells us if we need to return >> and sets up the exit_reason for us. >> >> Signed-off-by: Alex Bennée <alex.ben...@linaro.org> >> >> --- >> v2 >> - call helper directly from kvm_arch_vcpu_ioctl_run >> --- >> virt/kvm/arm/arm.c | 3 +++ >> 1 file changed, 3 insertions(+) >> >> diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c >> index 95cba0799828..2991adfaca9d 100644 >> --- a/virt/kvm/arm/arm.c >> +++ b/virt/kvm/arm/arm.c >> @@ -625,6 +625,9 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, >> struct kvm_run *run) >> ret = kvm_handle_mmio_return(vcpu, vcpu->run); >> if (ret) >> return ret; >> + if (kvm_arm_handle_step_debug(vcpu, vcpu->run)) >> + return 1; >> + > > In the previous patch, kvm_arch_vcpu_ioctl_run return 0 when telling > userspace about a debug exception. Shouldn't this branch return 0 > instead of 1?
Probably - although in practice it makes no difference. In QEMU for example the test is if (run_ret < 0) to handle errors. Otherwise success is assumed. > Returning on non-zero for kvm_handle_mmio_return is done because it > means there was an error. This is not the case for > kvm_arm_handle_step_debug. > > The description in the comment of kvm_arch_vcpu_ioctl_run is not very > clear whether non-zero result should be used for errors or if only the > negative values are treated as such, and positive values seems to be > generally used to keep the vcpu going. So, I thought it might make > sense to always return the same value upon debug exceptions. There is a subtle mis-match between what gets passed back to the ioctl and what terminates the while() loop later on. As far as the ioctl is concerned it's 0 success and - error. Once you get to the while loop you'll only ever exit once ret is no longer > 0. Anyway for consistency we should certainly return 0, I'll fix it on the next iteration. > > Cheers, -- Alex Bennée _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
