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

[Peter Xu]

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/

Thanks,

-- 
Peter Xu