Re: [PATCH] iommu/vt-d: Handle hotplug devices' default identity mapping setting

[James Dong via iommu <iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org>]

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Baolu:

Thanks for your comments and your patch. Please find below our responses to
each of your comments:

> What does "I/O operation won't work" exactly mean here? Do you see any
> IOMMU fault message? Or, something doesn't work as expected?

Yes, DMAR fault messages as following came out:
[  354.939896] DMAR: DMAR:[DMA Read] Request device [03:00.1]fault addr
1fdfe80000
[  354.939896] DMAR:[fault reason 02] Present bit in context entry is clear


> Do you mind checking this?
>
> index 6ecdcf8fc8c0..f62f30bc1339 100644
> --- a/drivers/iommu/intel-iommu.c
> +++ b/drivers/iommu/intel-iommu.c
> @@ -2632,6 +2632,9 @@ static struct dmar_domain
> *find_or_alloc_domain(struct device *dev, int gaw)
>                          goto out;
>          }
>
> +       if (!iommu_should_identity_map(dev, 0))
> +               return si_domain;
> +
>          /* Allocate and initialize new domain for the device */
>          domain = alloc_domain(0);
>          if (!domain)

Tried this patch, and the same DMAR fault message came out.

Guess it is because of the iommu code path for hotplug devices. If a hotplug
device is rescanned after removal, iommu_bus_notifier will be called as part
of the notifier chains to handle BUS_NOTIFY_ADD_DEVICE event. Along the code
path, intel_iommu_ops->add_device() created an iommu group for this hotplug
device, but failed to create an iommu domain because of the default domain
type IOMMU_DOMAIN_IDENTITY imposed by current IOMMU command line option got
declined by intel_iommu_ops->domain_alloc().

In your patch, function find_or_alloc_domain() is not even in the code path
of BUS_NOTIFY_ADD_DEVICE event notifier chain.

Please let us know if your have more concerns and suggestions.

Best Regards,
James

On Thu, Feb 21, 2019 at 9:35 PM Lu Baolu <baolu.lu-VuQAYsv1563Yd54FQh9/CA@public.gmane.org> wrote:

> Hi
>
> On 2/22/19 1:06 PM, Lu Baolu wrote:
>
> > Do you mind checking this?
> >
> > diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> > index 6ecdcf8fc8c0..f62f30bc1339 100644
> > --- a/drivers/iommu/intel-iommu.c
> > +++ b/drivers/iommu/intel-iommu.c
> > @@ -2632,6 +2632,9 @@ static struct dmar_domain
> > *find_or_alloc_domain(struct device *dev, int gaw)
> >                          goto out;
> >          }
> >
> > +       if (!iommu_should_identity_map(dev, 0))
> > +               return si_domain;
> > +
> >          /* Allocate and initialize new domain for the device */
> >          domain = alloc_domain(0);
> >          if (!domain)
>
> Oops! This can't be compiled. Please try below instead if you'd like to.
> Sorry about it.
>
> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> index 6ecdcf8fc8c0..b89f5ba6a3c8 100644
> --- a/drivers/iommu/intel-iommu.c
> +++ b/drivers/iommu/intel-iommu.c
> @@ -174,6 +174,8 @@ static inline unsigned long virt_to_dma_pfn(void *p)
>          return page_to_dma_pfn(virt_to_page(p));
>   }
>
> +static int iommu_should_identity_map(struct device *dev, int startup);
> +
>   /* global iommu list, set NULL for ignored DMAR units */
>   static struct intel_iommu **g_iommus;
>
> @@ -2632,6 +2634,9 @@ static struct dmar_domain
> *find_or_alloc_domain(struct device *dev, int gaw)
>                          goto out;
>          }
>
> +       if (iommu_should_identity_map(dev, 0))
> +               return si_domain;
> +
>          /* Allocate and initialize new domain for the device */
>          domain = alloc_domain(0);
>          if (!domain)
>
> Best regards,
> Lu Baolu
>
>
>

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