Re: [Qemu-devel] [PATCH 2/2 V5] qemu-kvm: fix improper nmi emulation

[Jan Kiszka]

On 2011-10-14 11:03, Lai Jiangshan wrote:
> 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 masked 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 enabled and KVM_SET_LINT1 is enabled,
>   inject LINT1 instead of NMI interrupt.
> 
> - otherwise 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.
> 
> - otherwise, userland lapic emulates NMI button and inject NMI
>   if it is unmasked.
> 
> Signed-off-by: Lai Jiangshan <address@hidden>
> Reported-by: Kenji Kaneshige <address@hidden>
> ---
>  hw/apic.c |   72 
> +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  hw/apic.h |    1 +
>  monitor.c |    6 ++++-
>  3 files changed, 78 insertions(+), 1 deletions(-)
> 
> diff --git a/hw/apic.c b/hw/apic.c
> index 69d6ac5..91b82d0 100644
> --- a/hw/apic.c
> +++ b/hw/apic.c
> @@ -205,6 +205,78 @@ void apic_deliver_pic_intr(DeviceState *d, int level)
>      }
>  }
>  
> +#ifdef KVM_CAP_IRQCHIP

Please read all my comments. That unfortunately also applies to the rest
of the patch.

> +static inline uint32_t kapic_reg(struct kvm_lapic_state *kapic, int reg_id);
> +
> +static void kvm_irqchip_deliver_nmi(void *p)
> +{
> +    APICState *s = p;
> +    struct kvm_lapic_state klapic;
> +    uint32_t lvt;
> +
> +    kvm_get_lapic(s->cpu_env, &klapic);
> +    lvt = kapic_reg(&klapic, 0x32 + APIC_LVT_LINT1);
> +
> +    if (lvt & APIC_LVT_MASKED) {
> +        return;
> +    }
> +
> +    if (((lvt >> 8) & 7) != APIC_DM_NMI) {
> +        return;
> +    }
> +
> +    kvm_vcpu_ioctl(s->cpu_env, KVM_NMI);
> +}
> +
> +static void __apic_deliver_nmi(APICState *s)
> +{
> +    if (kvm_irqchip_in_kernel()) {
> +        run_on_cpu(s->cpu_env, kvm_irqchip_deliver_nmi, s);
> +    } else {
> +        apic_local_deliver(s, APIC_LVT_LINT1);
> +    }
> +}
> +#else
> +static void __apic_deliver_nmi(APICState *s)
> +{
> +    apic_local_deliver(s, APIC_LVT_LINT1);
> +}
> +#endif
> +
> +enum {
> +    KVM_SET_LINT1_UNKNOWN,
> +    KVM_SET_LINT1_ENABLED,
> +    KVM_SET_LINT1_DISABLED,
> +};
> +
> +static void kvm_set_lint1(void *p)
> +{
> +    CPUState *env = p;
> +
> +    kvm_vcpu_ioctl(env, KVM_SET_LINT1);
> +}
> +
> +void apic_deliver_nmi(DeviceState *d)
> +{
> +    APICState *s = DO_UPCAST(APICState, busdev.qdev, d);
> +    static int kernel_lint1 = KVM_SET_LINT1_UNKNOWN;
> +
> +    if (kernel_lint1 == KVM_SET_LINT1_UNKNOWN) {
> +        if (kvm_enabled() && kvm_irqchip_in_kernel() &&
> +            kvm_check_extension(kvm_state, KVM_CAP_SET_LINT1)) {

That CAP test belongs where the injection shall happen. Here you decide
about user space vs. kernel space APIC model.

Let's try it together:

if kvm_enabled && kvm_irqchip_in_kernel
        run_on_cpu(kvm_apic_deliver_nmi)
else
        apic_local_deliver(APIC_LVT_LINT1)

with kvm_acpi_deliver_nmi like this:

if !check_extention(CAP_SET_LINT1)
        get_kernel_apic_state
        if !nmi_acceptable
                return
kvm_vcpu_ioctl(KVM_NMI)

Please don't trust me blindly and re-check, but this is how the scenario
looks like to me.

Thanks for your patience,
Jan

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