Commit 15dd29ca authored by Nicolin Chen's avatar Nicolin Chen Committed by Joerg Roedel
Browse files

iommu: Warn on premature unblock during DMA aliased sibling reset 



When two aliased siblings are in the same iommu_group, they might share the
same RID. The reset functions don't support this case, though it is unclear
whether there is a real case of having an ATS capable device on a PCI/PCI-X
bus.

Theoretically, however, if two aliased devices are resetting concurrently,
one might be unblocked prematurely in the middle of the reset by the other
sibling who completes the reset first.

This isn't a regression from this series but it's better to spit a warning,
so we can know if such use case is common enough for us to make subsequent
patches for its coverage.

Signed-off-by: default avatarNicolin Chen <nicolinc@nvidia.com>
Reviewed-by: default avatarKevin Tian <kevin.tian@intel.com>
Signed-off-by: default avatarJoerg Roedel <joerg.roedel@amd.com>
parent 5474e6e1

drivers/iommu/iommu.c

+49 −0
Original line number Diff line number Diff line
@@ -4105,6 +4105,41 @@ int pci_dev_reset_iommu_prepare(struct pci_dev *pdev) 
}

EXPORT_SYMBOL_GPL(pci_dev_reset_iommu_prepare);



static int __group_device_cmp_dma_alias(struct pci_dev *dev, u16 alias,

					void *data)

{

	return alias == *(u16 *)data;

}



static int group_device_cmp_dma_alias(struct pci_dev *dev, u16 alias,

				      void *data)

{

	return pci_for_each_dma_alias(data, __group_device_cmp_dma_alias,

				      &alias);

}



static bool group_device_dma_alias_is_blocked(struct iommu_group *group,

					      struct group_device *gdev)

{

	struct group_device *sibling;



	lockdep_assert_held(&group->mutex);



	if (!dev_is_pci(gdev->dev))

		return false;



	for_each_group_device(group, sibling) {

		if (sibling == gdev || !sibling->blocked ||

		    !dev_is_pci(sibling->dev))

			continue;

		if (pci_for_each_dma_alias(to_pci_dev(gdev->dev),

					   group_device_cmp_dma_alias,

					   to_pci_dev(sibling->dev)))

			return true;

	}

	return false;

}



/**

 * pci_dev_reset_iommu_done() - Restore IOMMU after a PCI device reset is done

 * @pdev: PCI device that has finished a reset routine
@@ -4144,6 +4179,20 @@ void pci_dev_reset_iommu_done(struct pci_dev *pdev) 
	if (WARN_ON(!group->blocking_domain))

		return;



	if (group_device_dma_alias_is_blocked(group, gdev)) {

		/*

		 * FIXME: DMA aliased devices share the same RID, which would be

		 * convoluted to handle, as "gdev->blocked" is not sufficient:

		 *  - "blocked" state is effectively shared across these devices

		 *  - if the core skipped the blocking on the second device, the

		 *    IOMMU driver's attachment state would diverge from the HW

		 *    state

		 * For now, just warn and see whether real ATS use cases hit it.

		 */

		pci_warn(pdev,

			 "DMA-aliased sibling may be prematurely unblocked\n");

	}



	/*

	 * Re-attach RID domain back to group->domain

	 *