Re: [Qemu-devel] [PATCH 1/1 V4] qemu-kvm: fix improper nmi emulation

[Lai Jiangshan <laijs@cn.fujitsu.com>]

On 10/14/2011 02:49 PM, Jan Kiszka wrote:
> On 2011-10-14 08:36, Lai Jiangshan wrote:
>> On 10/14/2011 01:53 PM, Jan Kiszka wrote:
>>> On 2011-10-14 02:53, Lai Jiangshan wrote:
>>>>
>>>>>
>>>>> As explained in some other mail, we could then emulate the missing
>>>>> kernel feature by reading out the current in-kernel APIC state, testing
>>>>> if LINT1 is unmasked, and then delivering the NMI directly.
>>>>>
>>>>
>>>> Only the thread of the VCPU can safely get the in-kernel LAPIC states,
>>>> so this approach will cause some troubles.
>>>
>>> run_on_cpu() can help.
>>>
>>> Jan
>>>
>>
>> Ah, I forgot it, Thanks.
>>
>> From: Lai Jiangshan <laijs@cn.fujitsu.com>
>>
>> Currently, NMI interrupt is blindly sent to all the vCPUs when NMI
>> button event happens. This doesn't properly emulate real hardware on
>> which NMI button event triggers LINT1. Because of this, NMI is sent to
>> the processor even when LINT1 is maskied in LVT. For example, this
>> causes the problem that kdump initiated by NMI sometimes doesn't work
>> on KVM, because kdump assumes NMI is masked on CPUs other than CPU0.
>>
>> With this patch, inject-nmi request is handled as follows.
>>
>> - When in-kernel irqchip is disabled, deliver LINT1 instead of NMI
>>   interrupt.
>> - When in-kernel irqchip is enabled, get the in-kernel LAPIC states
>>   and test the APIC_LVT_MASKED, if LINT1 is unmasked, and then
>>   delivering the NMI directly. (Suggested by Jan Kiszka)
>>
>> Changed from old version:
>>   re-implement it by the Jan's suggestion.
>>
>> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
>> Reported-by: Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
>> ---
>>  hw/apic.c |   48 ++++++++++++++++++++++++++++++++++++++++++++++++
>>  hw/apic.h |    1 +
>>  monitor.c |    6 +++++-
>>  3 files changed, 54 insertions(+), 1 deletions(-)
>> diff --git a/hw/apic.c b/hw/apic.c
>> index 69d6ac5..9a40129 100644
>> --- a/hw/apic.c
>> +++ b/hw/apic.c
>> @@ -205,6 +205,54 @@ void apic_deliver_pic_intr(DeviceState *d, int level)
>>      }
>>  }
>>  
>> +#ifdef KVM_CAP_IRQCHIP
> 
> Again, this is always defined on x86 thus pointless to test.
> 
>> +static inline uint32_t kapic_reg(struct kvm_lapic_state *kapic, int reg_id);
>> +
>> +struct kvm_get_remote_lapic_params {
>> +    CPUState *env;
>> +    struct kvm_lapic_state klapic;
>> +};
>> +
>> +static void kvm_get_remote_lapic(void *p)
>> +{
>> +    struct kvm_get_remote_lapic_params *params = p;
>> +
>> +    kvm_get_lapic(params->env, &params->klapic);
> 
> When you already interrupted that vcpu, why not inject from here? Avoids
> one further ping-pong round.

get_remote_lapic and inject nmi are two different things,
so I don't inject nmi from here. I didn't notice this ping-pond overhead.
Thank you.

> 
>> +}
>> +
>> +void apic_deliver_nmi(DeviceState *d)
>> +{
>> +    APICState *s = DO_UPCAST(APICState, busdev.qdev, d);
>> +
>> +    if (kvm_irqchip_in_kernel()) {
>> +        struct kvm_get_remote_lapic_params p = {.env = s->cpu_env,};
>> +        uint32_t lvt;
>> +
>> +        run_on_cpu(s->cpu_env, kvm_get_remote_lapic, &p);
>> +        lvt = kapic_reg(&p.klapic, 0x32 + APIC_LVT_LINT1);
>> +
>> +        if (lvt & APIC_LVT_MASKED) {
>> +            return;
>> +        }
>> +
>> +        if (((lvt >> 8) & 7) != APIC_DM_NMI) {
>> +            return;
>> +        }
>> +
>> +        cpu_interrupt(s->cpu_env, CPU_INTERRUPT_NMI);
> 
> Err, aren't you introducing KVM_CAP_LAPIC_NMI that allows to test if
> this workaround is needed? Oh, your latest kernel patch is missing this
> again - requires fixing as well.
> 


Kernel site patch is dropped with this v4 patch.

Did you mean you want KVM_CAP_SET_LINT1 + KVM_SET_LINT1 patches?
I have made them.

Sent soon.

Thanks,
Lai