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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: Nicolin Chen --- drivers/iommu/iommu.c | 49 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 49 insertions(+) diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c index f21d352a67f70..dd53cce12087c 100644 --- a/drivers/iommu/iommu.c +++ b/drivers/iommu/iommu.c @@ -4057,6 +4057,41 @@ 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 @@ -4096,6 +4131,20 @@ 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 * -- 2.43.0