Windows 11 blocks our custom Thunderbolt 4 PCIe hardware because of IOMMU memory isolation.

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Windows 11 blocks our custom Thunderbolt 4 PCIe hardware because of IOMMU memory isolation.

Jie Jun 60

We're looking for the recommended process to:

trace blocked DMA devices
map custom hardware IDs
approve trusted Thunderbolt 4 peripherals under Windows 11 DMA protection

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Answer 1

Hi Jie Jun,

Windows 11 Kernel DMA Protection secures Thunderbolt 4 peripherals by requiring drivers that support IOMMU DMA remapping, which can be verified in Device Manager if the DMA Remapping Policy value is two. Incompatible devices blocked by the system are tracked in the Event Viewer under Event ID 411. To manage these devices or map trusted custom hardware exceptions, administrators can configure the DeviceEnumerationPolicy registry key (under HKLM\Software\Policies\Microsoft\Windows\DmaGuard) to either completely block, entirely allow, or restrict device enumeration until a user logs in, while utilizing explicit allowlist policies for legacy hardware IDs.

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VPHAN