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 10:55:57 -0200
Eduardo Habkost <address@hidden> wrote:

> On Tue, Oct 18, 2016 at 02:44:55PM +0200, Igor Mammedov wrote:
> > 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.  
> 
> I see.
> 
> > 
> > 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");  
> 
> If there could be other iommu devices in the future, we can show
> it as an example, but not an instruction to be followed as-is.
> 
> Maybe we can just say "You can add an IOMMU using:
> -device intel-iommu,intremap=on,eim=on". It would mean it is one
> way to add an IOMMU, but not necessarily the only way.
ok, I'll amend error message.

> 
> BTW, are there any plans to make machine code create an IOMMU
> automatically if the VM config requires it?
not that I know of