Re: [PATCH 1/3] intel-iommu: fail MAP notifier without caching mode

[Jason Wang <jasowang@redhat.com>]

On Wed, Nov 30, 2022 at 11:06 PM Peter Xu <peterx@redhat.com> wrote:
>
> On Wed, Nov 30, 2022 at 02:23:06PM +0800, Jason Wang wrote:
> > On Tue, Nov 29, 2022 at 11:35 PM Peter Xu <peterx@redhat.com> wrote:
> > >
> > > On Tue, Nov 29, 2022 at 04:10:35PM +0800, Jason Wang wrote:
> > > > Without caching mode, MAP notifier won't work correctly since guest
> > > > won't send IOTLB update event when it establishes new mappings in the
> > > > I/O page tables. Let's fail the IOMMU notifiers early instead of
> > > > misbehaving silently.
> > > >
> > > > Signed-off-by: Jason Wang <jasowang@redhat.com>
> > > > ---
> > > >  hw/i386/intel_iommu.c | 7 +++++++
> > > >  1 file changed, 7 insertions(+)
> > > >
> > > > diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
> > > > index a08ee85edf..9143376677 100644
> > > > --- a/hw/i386/intel_iommu.c
> > > > +++ b/hw/i386/intel_iommu.c
> > > > @@ -3186,6 +3186,13 @@ static int vtd_iommu_notify_flag_changed(IOMMUMemoryRegion *iommu,
> > > >                           "Snoop Control with vhost or VFIO is not supported");
> > > >          return -ENOTSUP;
> > > >      }
> > > > +    if (!s->caching_mode && (new & IOMMU_NOTIFIER_MAP)) {
> > > > +        error_setg_errno(errp, ENOTSUP,
> > > > +                         "device %02x.%02x.%x requires caching mode",
> > > > +                         pci_bus_num(vtd_as->bus), PCI_SLOT(vtd_as->devfn),
> > > > +                         PCI_FUNC(vtd_as->devfn));
> > > > +        return -ENOTSUP;
> > > > +    }
> > >
> > > We used to have that but got reverted because it's too late to fail, so we
> > > moved it over even though not as clean..
> > >
> > > https://lore.kernel.org/all/20190916080718.3299-5-peterx@redhat.com/
> >
> > One of the difference is that the patch doesn't do exit() here. I
> > think it's better to fail instead of misbehving silently, this is what
> > other vIOMMU did:
> >
> > E.g in smmu we had:
> >
> >     if (new & IOMMU_NOTIFIER_MAP) {
> >         error_setg(errp,
> >                    "device %02x.%02x.%x requires iommu MAP notifier which is "
> >                    "not currently supported", pci_bus_num(sdev->bus),
> >                    PCI_SLOT(sdev->devfn), PCI_FUNC(sdev->devfn));
> >         return -EINVAL;
> >     }
> >
> > So did for amd iommu.
>
> Yeah that's fine.  Would you mind add the explanation (and also above link,
> which might be helpful to pick up the history..) to the commit message?

Will do.

> With that:
>
> Reviewed-by: Peter Xu <peterx@redhat.com>
>
> Thanks,

Thanks

>
> --
> Peter Xu
>