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

[Jan Kiszka <jan.kiszka@web.de>]

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On 2012-02-11 11:02, Blue Swirl wrote:
> On Fri, Feb 10, 2012 at 18:31, Jan Kiszka <jan.kiszka@siemens.com> 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.

I did check this before changing, and I see no such need. Particularly
as this old debugging help prevents valid use case.

Jan

> 
>> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
>> ---
>>  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
>>
>>
> 
> 



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