Re: [Qemu-devel] [PATCH] KVM: Don't assume that mpstate exists with in-kernel PIC always

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

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On 2013-04-25 18:46, Alexander Graf wrote:
> 
> On 25.04.2013, at 18:13, Jan Kiszka wrote:
> 
>> On 2013-04-25 11:06, Alexander Graf wrote:
>>> On PPC, we don't support MP state. So far it's not necessary and I'm
>>> not convinced yet that we really need to support it ever.
>>>
>>> However, the current idle logic in QEMU assumes that an in-kernel PIC
>>> also means we support MP state. This assumption is not true anymore.
>>>
>>> Let's split up the two cases into two different variables. That way
>>> PPC can expose an in-kernel PIC, while not implementing MP state.
>>>
>>> Signed-off-by: Alexander Graf <agraf@suse.de>
>>> CC: Jan Kiszka <jan.kiszka@siemens.com>
>>>
>>> ---
>>>
>>> v1 -> v2:
>>>
>>>  - use kvm_halt_in_kernel() instead
>>> ---
>>> cpus.c               |    2 +-
>>> include/sysemu/kvm.h |   10 ++++++++++
>>> kvm-all.c            |    2 ++
>>> 3 files changed, 13 insertions(+), 1 deletions(-)
>>>
>>> diff --git a/cpus.c b/cpus.c
>>> index e919dd7..e626f7e 100644
>>> --- a/cpus.c
>>> +++ b/cpus.c
>>> @@ -73,7 +73,7 @@ static bool cpu_thread_is_idle(CPUArchState *env)
>>>         return true;
>>>     }
>>>     if (!cpu->halted || qemu_cpu_has_work(cpu) ||
>>> -        kvm_async_interrupts_enabled()) {
>>> +        kvm_halt_in_kernel()) {
>>>         return false;
>>>     }
>>>     return true;
>>> diff --git a/include/sysemu/kvm.h b/include/sysemu/kvm.h
>>> index 8a9ebda..07375bf 100644
>>> --- a/include/sysemu/kvm.h
>>> +++ b/include/sysemu/kvm.h
>>> @@ -42,6 +42,7 @@
>>> extern bool kvm_allowed;
>>> extern bool kvm_kernel_irqchip;
>>> extern bool kvm_async_interrupts_allowed;
>>> +extern bool kvm_halt_in_kernel_allowed;
>>> extern bool kvm_irqfds_allowed;
>>> extern bool kvm_msi_via_irqfd_allowed;
>>> extern bool kvm_gsi_routing_allowed;
>>> @@ -72,6 +73,14 @@ extern bool kvm_gsi_routing_allowed;
>>> #define kvm_async_interrupts_enabled() (kvm_async_interrupts_allowed)
>>>
>>> /**
>>> + * kvm_supports_mpstate:
>>> + *
>>> + * Returns: true if the kvm side supports MP states which is
>>> + * required to indicate to kvm that a vcpu is currently halted
>>
>> "...and make KVM wait for resumption inside the kernel instead for
>> reporting halt to userspace." Or so.
>>
>> That's why I asked for calling this helper differently: to express the
>> concept behind it, not the implementation detail "mpstate" (which is an
>> x86-caused misnomer).
> 
> It's not exactly a misnomer. It's a concept that is required to implement the logic. I've updated the comment accordingly :).

AFAIK, the concept ("multi-processor state") was introduced for and
named after x86 properties.

Jan



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