Re: [PATCH v4 1/3] xen/x86: add nmi continuation framework

[Jürgen Groß <jgross@xxxxxxxx>]

On 11.11.20 16:37, Jan Beulich wrote:
> On 09.11.2020 10:50, Juergen Gross wrote:
> > Actions in NMI context are rather limited as e.g. locking is rather
> > fragile.
> >
> > Add a framework to continue processing in normal interrupt context
> > after leaving NMI processing.
> >
> > This is done by a high priority interrupt vector triggered via a
> > self IPI from NMI context, which will then call the continuation
> > function specified during NMI handling.
> >
> > Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
> with one further adjustment request:
>
> > @@ -1799,6 +1800,24 @@ void unset_nmi_callback(void)
> >       nmi_callback = dummy_nmi_callback;
> >   }
> >   
> > +bool nmi_check_continuation(void)
> > +{
> > +    bool ret = false;
> > +
> > +    return ret;
> > +}
> > +
> > +void trigger_nmi_continuation(void)
> > +{
> > +    /*
> > +     * Issue a self-IPI. Handling is done in spurious_interrupt().
> > +     * NMI could have happened in IPI sequence, so wait for ICR being idle
> > +     * again before leaving NMI handler.
> > +     */
> > +    send_IPI_self(SPURIOUS_APIC_VECTOR);
> > +    apic_wait_icr_idle();
> > +}
> This additionally relies on send_IPI_self_legacy() calling
> send_IPI_shortcut(), rather than e.g. resolving the local CPU
> number to a destination ID. I think this wants saying maybe
> here, but more importantly in that function.
Okay.


Juergen

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