Re: [PATCH] iommu/intel-iommu: set as DUMMY_DEVICE_DOMAIN_INFO if no IOMMU

[Lu Baolu]

Hi,

On 2020/2/4 17:25, Jian-Hong Pan wrote:
> Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx> æ 2020å2æ4æ éä äå2:11åéï
> > Hi,
> >
> > On 2020/2/3 17:10, Jian-Hong Pan wrote:
> > > If the device has no IOMMU, it still invokes iommu_need_mapping during
> > > intel_alloc_coherent. However, iommu_need_mapping can only check the
> > > device is DUMMY_DEVICE_DOMAIN_INFO or not. This patch marks the device
> > > is a DUMMY_DEVICE_DOMAIN_INFO if the device has no IOMMU.
> > >
> > > Signed-off-by: Jian-Hong Pan <jian-hong@xxxxxxxxxxxx>
> > > ---
> > >    drivers/iommu/intel-iommu.c | 4 +++-
> > >    1 file changed, 3 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> > > index 35a4a3abedc6..878bc986a015 100644
> > > --- a/drivers/iommu/intel-iommu.c
> > > +++ b/drivers/iommu/intel-iommu.c
> > > @@ -5612,8 +5612,10 @@ static int intel_iommu_add_device(struct device *dev)
> > >        int ret;
> > >
> > >        iommu = device_to_iommu(dev, &bus, &devfn);
> > > -     if (!iommu)
> > > +     if (!iommu) {
> > > +             dev->archdata.iommu = DUMMY_DEVICE_DOMAIN_INFO;
> >
> > Is this a DMA capable device?
>
> Do you mean is the device in DMA Remapping table?
> Dump DMAR from ACPI table.  The device is not in the table.
> So, it does not support DMAR, Intel IOMMU.
>
> Or, should device_to_iommu be invoked in iommu_need_mapping to check
> IOMMU feature again?

Normally intel_iommu_add_device() should only be called for PCI devices
and APCI name space devices (reported in ACPI/DMAR table). In both
cases, device_to_iommu() should always return a corresponding iommu. I
just tried to understand why it failed for your case.

Best regards,
baolu