On Wed, Jan 31, 2018 at 9:13 AM, Paolo Bonzini <pbonz...@redhat.com> wrote: > 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.
The problem with that is that I hit this assert for ARM CPUs: qemu-system-aarch64: ./target/arm/cpu.h:1446: arm_el_is_aa64: Assertion `el >= 1 && el <= 3' failed. Alistair > > 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 >> >
