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Re: [Qemu-devel] MTTCG External Halt
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] MTTCG External Halt |
Date: |
Wed, 31 Jan 2018 12:13:19 -0500 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.2 |
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
>
- Re: [Qemu-devel] MTTCG External Halt, (continued)
- Re: [Qemu-devel] MTTCG External Halt, Peter Maydell, 2018/01/03
- Re: [Qemu-devel] MTTCG External Halt, Alex Bennée, 2018/01/04
- Re: [Qemu-devel] MTTCG External Halt, Alistair Francis, 2018/01/05
- Re: [Qemu-devel] MTTCG External Halt, Alistair Francis, 2018/01/30
- Re: [Qemu-devel] MTTCG External Halt, Paolo Bonzini, 2018/01/30
- Re: [Qemu-devel] MTTCG External Halt, Alistair Francis, 2018/01/31
- Re: [Qemu-devel] MTTCG External Halt, Alex Bennée, 2018/01/31
- Re: [Qemu-devel] MTTCG External Halt, Alistair Francis, 2018/01/31
Re: [Qemu-devel] MTTCG External Halt,
Paolo Bonzini <=
- Re: [Qemu-devel] MTTCG External Halt, Alistair Francis, 2018/01/31
- Re: [Qemu-devel] MTTCG External Halt, Peter Maydell, 2018/01/31
- Re: [Qemu-devel] MTTCG External Halt, Alistair Francis, 2018/01/31
- Re: [Qemu-devel] MTTCG External Halt, Alistair Francis, 2018/01/31
- Re: [Qemu-devel] MTTCG External Halt, Peter Maydell, 2018/01/31
- Re: [Qemu-devel] MTTCG External Halt, Alistair Francis, 2018/01/31