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

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

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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.

> +}
> +
> +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.

Jan


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