When IOMMU is not enabled, any PCIe device capable of DMA could access arbitrary physical memory. It allows to read any sensitive data, modifying memory and fully compromising the system without CPU involvement.

There are many DMA-based attacks described in the literature. Even with IOMMU, some attacks are still possible due to misconfiguration or incomplete isolation. For example: https://www.repository.cam.ac.uk/items/13dcaac4-5a3d-4f67-82...

In our case, we didn’t dive deeply into the security aspects. Our typical deployment assumes a trusted environment where YDB runs on dedicated hardware, so performance considerations tend to dominate.