https://nalar.dev/tags/acs/ Recent content in ACS on Nalar Hugo en-us Sat, 19 Sep 2026 00:00:00 +0000 https://nalar.dev/pcie-acs-controls-peer-traffic-bypass-iommu/ Sat, 19 Sep 2026 00:00:00 +0000 https://nalar.dev/pcie-acs-controls-peer-traffic-bypass-iommu/ <h1 id="pcie-acs-controls-whether-peer-traffic-can-bypass-the-iommu">PCIe ACS Controls Whether Peer Traffic Can Bypass the IOMMU</h1> <p>An IOMMU can restrict DMA only for transactions that reach its translation and permission checks. PCI Express complicates that boundary because two endpoints under the same hierarchy can exchange peer-to-peer traffic without sending every transaction through the root complex. A switch may be able to route a request directly from one downstream port to another.</p> <p>PCIe Access Control Services (ACS) adds controls for that routing boundary. Depending on the component and supported ACS features, the fabric can validate a request, block selected translated traffic, redirect peer requests or completions upstream, or constrain their egress. The result is not merely a routing preference. ACS can determine whether two devices are separable at the IOMMU boundary.</p>