Re: [Qemu-devel] [PATCH v2 1/8] kvm: Set cpu_single_env only once

[Blue Swirl]

On Fri, Feb 10, 2012 at 18:31, Jan Kiszka <address@hidden> wrote:
> As we have thread-local cpu_single_env now and KVM uses exactly one
> thread per VCPU, we can drop the cpu_single_env updates from the loop
> and initialize this variable only once during setup.

I don't think this is correct. Maybe you missed the part that sets
cpu_single_env to NULL, which I think is to annoy broken code that
assumes that some CPU state is always globally available. This is not
true for monitor context.

> Signed-off-by: Jan Kiszka <address@hidden>
> ---
>  cpus.c    |    1 +
>  kvm-all.c |    5 -----
>  2 files changed, 1 insertions(+), 5 deletions(-)
>
> diff --git a/cpus.c b/cpus.c
> index f45a438..d0c8340 100644
> --- a/cpus.c
> +++ b/cpus.c
> @@ -714,6 +714,7 @@ static void *qemu_kvm_cpu_thread_fn(void *arg)
>     qemu_mutex_lock(&qemu_global_mutex);
>     qemu_thread_get_self(env->thread);
>     env->thread_id = qemu_get_thread_id();
> +    cpu_single_env = env;
>
>     r = kvm_init_vcpu(env);
>     if (r < 0) {
> diff --git a/kvm-all.c b/kvm-all.c
> index c4babda..e2cbc03 100644
> --- a/kvm-all.c
> +++ b/kvm-all.c
> @@ -1118,8 +1118,6 @@ int kvm_cpu_exec(CPUState *env)
>         return EXCP_HLT;
>     }
>
> -    cpu_single_env = env;
> -
>     do {
>         if (env->kvm_vcpu_dirty) {
>             kvm_arch_put_registers(env, KVM_PUT_RUNTIME_STATE);
> @@ -1136,13 +1134,11 @@ int kvm_cpu_exec(CPUState *env)
>              */
>             qemu_cpu_kick_self();
>         }
> -        cpu_single_env = NULL;
>         qemu_mutex_unlock_iothread();
>
>         run_ret = kvm_vcpu_ioctl(env, KVM_RUN, 0);
>
>         qemu_mutex_lock_iothread();
> -        cpu_single_env = env;
>         kvm_arch_post_run(env, run);
>
>         kvm_flush_coalesced_mmio_buffer();
> @@ -1206,7 +1202,6 @@ int kvm_cpu_exec(CPUState *env)
>     }
>
>     env->exit_request = 0;
> -    cpu_single_env = NULL;
>     return ret;
>  }
>
> --
> 1.7.3.4
>
>