Re: [PATCH 1/8] iommu: Decouple iommu_present() from bus ops

From: Baolu Lu
Date: Thu Jan 26 2023 - 08:13:17 EST


On 2023/1/20 3:18, Robin Murphy wrote:
Much as I'd like to remove iommu_present(), the final remaining users
are proving stubbornly difficult to clean up, so kick that can down
the road and just rework it to preserve the current behaviour without
depending on bus ops.

Signed-off-by: Robin Murphy <robin.murphy@xxxxxxx>
---
drivers/iommu/iommu.c | 17 ++++++++++++++++-
1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index b189ed345057..a77d58e1b976 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -1871,9 +1871,24 @@ int bus_iommu_probe(struct bus_type *bus)
return ret;
}
+static int __iommu_present(struct device *dev, void *unused)
+{
+ return device_iommu_mapped(dev);
+}

/**
* device_iommu_mapped - Returns true when the device DMA is translated
* by an IOMMU
* @dev: Device to perform the check on
*/
static inline bool device_iommu_mapped(struct device *dev)
{
return (dev->iommu_group != NULL);
}

Perhaps device_iommu_mapped() should be improved. In some cases, the
device has an iommu_group filled is not enough to indicate that the
device has IOMMU hardware for DMA translation.

For example, VFIO could allocate an iommu_group and add a device into
the iommu_group even there's no IOMMU hardware in
vfio_noiommu_group_alloc().

Basically iommu_group_add_device() doesn't check the presence of an
IOMMU.

+
+/**
+ * iommu_present() - make platform-specific assumptions about an IOMMU
+ * @bus: bus to check
+ *
+ * Do not use this function. You want device_iommu_mapped() instead.
+ *
+ * Return: true if some IOMMU is present for some device on the given bus. In
+ * general it may not be the only IOMMU, and it may not be for the device you
+ * are ultimately interested in.
+ */
bool iommu_present(struct bus_type *bus)
{
- return bus->iommu_ops != NULL;
+ return bus_for_each_dev(bus, NULL, NULL, __iommu_present) > 0;
}
EXPORT_SYMBOL_GPL(iommu_present);

--
Best regards,
baolu