On 03/01/2018 17:10, Alistair Francis wrote: > Hey guys, I'm super stuck with an ugly MTTCG issue and was wondering > if anyone had any ideas. > > In the Xilinx fork of QEMU (based on 2.11) we have a way for CPUs to > halt other CPUs. This is used for example when the power control unit > halts the ARM A53s. To do this we have internal GPIO signals that end > up calling a function that basically does this: > > To halt: > cpu->halted = true; > cpu_interrupt(cpu, CPU_INTERRUPT_HALT);
cpu->halted = true should not be needed here. It will be set by cpu_handle_interrupt when processing CPU_INTERRUPT_HALT. > To un-halt > cpu->halted = false; > cpu_reset_interrupt(cpu, CPU_INTERRUPT_HALT); cpu->halted = false likewise should not be needed here, but you cannot just clear CPU_INTERRUPT_HALT either. You need to set a *different* interrupt request bit (the dummy CPU_INTERRUPT_EXITTB will do) and cpu_handle_halt will clear cpu->halted. Paolo > We also have the standard ARM WFI (Wait For Interrupt) implementation > in op_helper.c: > cs->halted = 1; > cs->exception_index = EXCP_HLT; > cpu_loop_exit(cs); > > Before MTTCG this used to work great, but now either we end up with > the guest Linux complaining about CPU stalls or we hit: > ERROR:/scratch/alistai/master-qemu/cpus.c:1516:qemu_tcg_cpu_thread_fn: > assertion failed: (cpu->halted) > > If I remove the instances of manually setting cpu->halted then I don't > see the asserts(), but the the WFI instruction doesn't work correctly. > So it seems like setting the halted status externally from the CPU > causes the issue. I have tried setting it inside a lock, using atomic > operations and running the setter async on the CPU, but nothing works. > > Any chance any one has some insight into a way to externally set a > vCPU as halted/un-halted? > > Thanks, > Alistair >
