Re: [Qemu-devel] [PATCH v4 13/13] pc: require IRQ remapping and EIM if there could be x2APIC CPUs

[Igor Mammedov]

On Tue, 18 Oct 2016 09:27:37 -0200
Eduardo Habkost <address@hidden> wrote:

> On Fri, Oct 14, 2016 at 01:25:35PM +0200, Igor Mammedov wrote:
> > it would prevent starting guest with incorrect configs
> > where interrupts couldn't be delivered to CPUs with
> > APIC IDs > 255.
> > 
> > Signed-off-by: Igor Mammedov <address@hidden>
> > Reviewed-by: Radim Krčmář <address@hidden>
> > ---
> > v4:
> >  - s/254/255/ in commit message (Radim)
> > ---
> >  hw/i386/pc.c | 13 +++++++++++++
> >  1 file changed, 13 insertions(+)
> > 
> > diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> > index 40eb43b..f7070e0 100644
> > --- a/hw/i386/pc.c
> > +++ b/hw/i386/pc.c
> > @@ -68,6 +68,7 @@
> >  #include "qapi-visit.h"
> >  #include "qom/cpu.h"
> >  #include "hw/nmi.h"
> > +#include "hw/i386/intel_iommu.h"
> >  
> >  /* debug PC/ISA interrupts */
> >  //#define DEBUG_IRQ
> > @@ -1264,6 +1265,18 @@ void pc_machine_done(Notifier *notifier, void *data)
> >                              sizeof(pcms->boot_cpus_le));
> >          }
> >      }
> > +
> > +    if (pcms->apic_id_limit > 255) {
> > +        IntelIOMMUState *iommu = 
> > INTEL_IOMMU_DEVICE(x86_iommu_get_default());
> > +
> > +        if (!iommu || !iommu->x86_iommu.intr_supported ||
> > +            iommu->intr_eim != ON_OFF_AUTO_ON) {
> > +            error_report("current -smp configuration requires "
> > +                         "Extended Interrupt Mode enabled. "
> > +                         "IOMMU should have eim=on option set");  
> 
> Suggestion for a follow-up patch:
> 
> * Error message explaining how to set eim=on if the iommu is
>   available
> * Error message explaining how to make sure the iommu is created,
>   in case it was not even created.
Reason I didn't include how to create iommu/CLI example is that
it could be some other iommu in future so that message could
bit rot over time.

But I can add description if you'd prefer it.
How about something like this:
+            error_report("current -smp configuration requires "
+                         "Intel IOMMU with Extended Interrupt Mode enabled. "
+                         "To enable IOMMU add to command line: "
+                         "-device intel-iommu,intremap=on,eim=on");