Re: [PATCH 3/3] iommu: prevent VMD child devices from being remapping targets
From: Robin Murphy
Date: Fri Aug 11 2017 - 14:26:01 EST
On 07/08/17 20:57, Jon Derrick wrote:
> VMD child devices must use the VMD endpoint's ID as the DMA source.
> Because of this, there needs to be a way to link the parent VMD
> endpoint's DMAR domain to the VMD child devices' DMAR domain such that
> attaching and detaching child devices modify the endpoint's DMAR mapping
> and prevents early detaching.
That sounds like either pci_device_group() needs modifying, or perhaps
that intel-iommu needs its own extended iommu_ops::device_group
implementation, to ensure that VMD child devices get put in the same
group as their parent - if they share requester IDs they can't feasibly
be attached to different domains anyway.
Robin.
> This is outside the scope of VMD, so disable binding child devices to
> prevent unforeseen issues. This functionality may be implemented in the
> future.
>
> This patch prevents VMD child devices from returning an IOMMU, which
> prevents it from exposing iommu_group sysfs directories and subsequent
> binding by userspace-access drivers such as VFIO.
>
> Signed-off-by: Jon Derrick <jonathan.derrick@xxxxxxxxx>
> ---
> drivers/iommu/intel-iommu.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> index 687f18f..651a6cd 100644
> --- a/drivers/iommu/intel-iommu.c
> +++ b/drivers/iommu/intel-iommu.c
> @@ -905,6 +905,11 @@ static struct intel_iommu *device_to_iommu(struct device *dev, u8 *bus, u8 *devf
> * the PF instead to find the IOMMU. */
> pf_pdev = pci_physfn(pdev);
> dev = &pf_pdev->dev;
> +
> + /* VMD child devices currently cannot be handled individually */
> + if (pci_bus_is_vmd(pdev->bus))
> + return NULL;
> +
> segment = pci_domain_nr(pdev->bus);
> } else if (has_acpi_companion(dev))
> dev = &ACPI_COMPANION(dev)->dev;
>