We encounter a issue with the patch: our platform is ARM64, and we run DPDK with smmu disable on VM (without iommu=smmuv3 etc),

so we use noiommu mode with enable_unsafe_noiommu_mode=1 to passthrough the device to VM with following steps (those steps are on VM) :

insmod vfio.ko enable_unsafe_noiommu_mode=1
insmod vfio_virqfd.ko
insmod vfio-pci-core.ko
insmdo vfio-pci.ko
insmod vfio_iommu_type1.ko

echo vfio-pci > /sys/bus/pci/devices/0000:00:02.0/driver_override
echo 0000:00:02.0 > /sys/bus/pci/drivers_probe ------------------ failed

I find that vfio-pci device is not probed because of the additional check. It works well without this patch.

Do we need to skip the check if enable_unsafe_noiommu_mode=1?

Best regards,

Xiang Chen

在 2022/4/11 23:16, Jason Gunthorpe 写道:
IOMMU_CACHE means that normal DMAs do not require any additional coherency
mechanism and is the basic uAPI that VFIO exposes to userspace. For
instance VFIO applications like DPDK will not work if additional coherency
operations are required.

Therefore check IOMMU_CAP_CACHE_COHERENCY like vdpa & usnic do before
allowing an IOMMU backed VFIO device to be created.

Reviewed-by: Kevin Tian <kevin.t...@intel.com>
Acked-by: Alex Williamson <alex.william...@redhat.com>
Acked-by: Robin Murphy <robin.mur...@arm.com>
Signed-off-by: Jason Gunthorpe <j...@nvidia.com>
  drivers/vfio/vfio.c | 7 +++++++
  1 file changed, 7 insertions(+)

diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
index a4555014bd1e72..9edad767cfdad3 100644
--- a/drivers/vfio/vfio.c
+++ b/drivers/vfio/vfio.c
@@ -815,6 +815,13 @@ static int __vfio_register_dev(struct vfio_device *device,
int vfio_register_group_dev(struct vfio_device *device)
+       /*
+        * VFIO always sets IOMMU_CACHE because we offer no way for userspace to
+        * restore cache coherency.
+        */
+       if (!iommu_capable(device->dev->bus, IOMMU_CAP_CACHE_COHERENCY))
+               return -EINVAL;
        return __vfio_register_dev(device,

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