Re: [PATCH] iommu/vt-d: Fix PCI bus rescan device hot add

[Lu Baolu]

On 1/14/22 11:11 AM, Jacob Pan wrote:
> On Fri, 14 Jan 2022 08:58:53 +0800, Lu Baolu<baolu.lu@xxxxxxxxxxxxxxx>
> wrote:
>
> > Hi Jacob,
> >
> > On 1/13/22 9:23 PM, Jacob Pan wrote:
> > > During PCI bus rescan, adding new devices involve two notifiers.
> > > 1. dmar_pci_bus_notifier()
> > > 2. iommu_bus_notifier()
> > > The current code sets #1 as low priority (INT_MIN) which resulted in #2
> > > being invoked first. The result is that struct device pointer cannot be
> > > found in DRHD search for the new device's DMAR/IOMMU. Subsequently, the
> > > device is put under the "catch-all" IOMMU instead of the correct one.
> > >
> > > This could cause system hang when device TLB invalidation is sent to the
> > > wrong IOMMU. Invalidation timeout error or hard lockup can be observed.
> > >
> > > This patch fixes the issue by setting a higher priority for
> > > dmar_pci_bus_notifier. DRHD search for a new device will find the
> > > correct IOMMU.
> > >
> > > Fixes: 59ce0515cdaf ("iommu/vt-d: Update DRHD/RMRR/ATSR device scope")
> > > Reported-by: Zhang, Bernice<bernice.zhang@xxxxxxxxx>
> > > Signed-off-by: Jacob Pan<jacob.jun.pan@xxxxxxxxxxxxxxx>
> > > ---
> > >    drivers/iommu/intel/dmar.c | 2 +-
> > >    1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/iommu/intel/dmar.c b/drivers/iommu/intel/dmar.c
> > > index 915bff76fe96..5d07e5b89c2e 100644
> > > --- a/drivers/iommu/intel/dmar.c
> > > +++ b/drivers/iommu/intel/dmar.c
> > > @@ -385,7 +385,7 @@ static int dmar_pci_bus_notifier(struct
> > > notifier_block *nb,
> > >    static struct notifier_block dmar_pci_bus_nb = {
> > >    	.notifier_call = dmar_pci_bus_notifier,
> > > -	.priority = INT_MIN,
> > > +	.priority = INT_MAX,
> > >    };
> > >    
> > >    static struct dmar_drhd_unit *
> > >    
> > Nice catch! dmar_pci_bus_add_dev() should take place*before*
> > iommu_probe_device(). This change enforces this with a higher notifier
> > priority for dmar callback.
> >
> > Comparably, dmar_pci_bus_del_dev() should take place*after*
> > iommu_release_device(). Perhaps we can use two notifiers, one for
> > ADD_DEVICE (with .priority=INT_MAX) and the other for REMOVE_DEVICE
> > (with .priority=INT_MIN)?
> Since device_to_iommu() lookup in intel_iommu_release_device() only
> checks if device is under "an" IOMMU, not "the" IOMMU. Then the remove path
> order is not needed, right?
>
> I know this is not robust, but having so many notifiers with implicit
> priority is not clean either.
>
> Perhaps, we should have explicit priority defined around iommu_bus
> notifier? i.e.
>
> @@ -1841,6 +1841,7 @@ static int iommu_bus_init(struct bus_type *bus, const
> struct iommu_ops *ops) return -ENOMEM;
>          nb->notifier_call = iommu_bus_notifier;
>                         
> +       nb->priority = IOMMU_BUS_NOTIFY_PRIORITY;
>                         
>
>   static struct notifier_block dmar_pci_bus_add_nb = {
>          .notifier_call = dmar_pci_bus_notifier,
> -       .priority = INT_MIN,
> +       .priority = IOMMU_BUS_NOTIFY_PRIORITY + 1,
>   };
>
>   static struct notifier_block dmar_pci_bus_remove_nb = {
>          .notifier_call = dmar_pci_bus_notifier,
> -       .priority = INT_MIN,
> +       .priority = IOMMU_BUS_NOTIFY_PRIORITY - 1,
>   };

IOMMU_BUS_NOTIFY_PRIORITY by default is 0. So you can simply use 1 and
-1? Adding a comment around it will be helpful.

Best regards,
baolu