Re: [Xen-devel] [PATCH 2/4] x86/nmi: enable local irqs in wait_for_nmis()

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 14.05.14 at 14:58, <david.vrabel@xxxxxxxxxx> wrote:
> --- a/xen/arch/x86/nmi.c
> +++ b/xen/arch/x86/nmi.c
> @@ -111,7 +111,14 @@ int nmi_active;
>  
>  static void __init wait_for_nmis(void *p)
>  {
> +    unsigned long flags;
> +
> +    local_save_flags(flags);
> +    local_irq_enable();
> +
>      mdelay((10*1000)/nmi_hz); /* wait 10 ticks */
> +
> +    local_irq_restore(flags);
>  }

This being the callback for on_selected_cpus(), i.e. called out of
interrupt context, I don't think it is uniformly safe to enable
interrupts here. The current behavior anyway is for the function
to run with interrupts enabled on the boot CPU, and with interrupts
disabled on the APs. So for this change to make a difference, the
IRQ would need to be bound to one of the APs, and consequently
the fix would be to force it onto the BP until boot progressed far
enough.

Jan


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