Philippe Mathieu-Daudé <philmd@xxxxxxxxxx> writes: > On 30/5/24 21:42, Alex Bennée wrote: >> Originally I tried to move where vCPU thread initialisation to later >> in realize. However pulling that thread (sic) got gnarly really >> quickly. It turns out some steps of CPU realization need values that >> can only be determined from the running vCPU thread. > > FYI: > https://lore.kernel.org/qemu-devel/20240528145953.65398-6-philmd@xxxxxxxxxx/ But this still has it in realize which would still race as the threads are started before we call the common realize functions. > >> However having moved enough out of the thread creation we can now >> queue work before the thread starts (at least for TCG guests) and >> avoid the race between vcpu_init and other vcpu states a plugin might >> subscribe to. >> Signed-off-by: Alex Bennée <alex.bennee@xxxxxxxxxx> >> --- >> hw/core/cpu-common.c | 20 ++++++++++++-------- >> 1 file changed, 12 insertions(+), 8 deletions(-) >> diff --git a/hw/core/cpu-common.c b/hw/core/cpu-common.c >> index 6cfc01593a..bf1a7b8892 100644 >> --- a/hw/core/cpu-common.c >> +++ b/hw/core/cpu-common.c >> @@ -222,14 +222,6 @@ static void cpu_common_realizefn(DeviceState *dev, Error **errp) >> cpu_resume(cpu); >> } >> - /* Plugin initialization must wait until the cpu start >> executing code */ >> -#ifdef CONFIG_PLUGIN >> - if (tcg_enabled()) { >> - cpu->plugin_state = qemu_plugin_create_vcpu_state(); >> - async_run_on_cpu(cpu, qemu_plugin_vcpu_init__async, RUN_ON_CPU_NULL); >> - } >> -#endif >> - >> /* NOTE: latest generic point where the cpu is fully realized */ >> } >> @@ -273,6 +265,18 @@ static void cpu_common_initfn(Object *obj) >> QTAILQ_INIT(&cpu->watchpoints); >> cpu_exec_initfn(cpu); >> + >> + /* >> + * Plugin initialization must wait until the cpu start executing >> + * code, but we must queue this work before the threads are >> + * created to ensure we don't race. >> + */ >> +#ifdef CONFIG_PLUGIN >> + if (tcg_enabled()) { >> + cpu->plugin_state = qemu_plugin_create_vcpu_state(); > > Per https://etherpad.opendev.org/p/QEMU_vCPU_life, plugin_state could > be initialized in AccelCPUClass::cpu_instance_init (although this > callback is called at CPUClass::instance_post_init which I haven't > yet figured why). Why are x86 and RiscV special in terms of calling this function? > >> + async_run_on_cpu(cpu, qemu_plugin_vcpu_init__async, RUN_ON_CPU_NULL); >> + } >> +#endif >> } >> static void cpu_common_finalize(Object *obj) -- Alex Bennée Virtualisation Tech Lead @ Linaro
