Hi Mario, On Tue, Mar 15, 2022 at 04:30:08PM -0500, Mario Limonciello wrote: > Historically TBT3 in Linux used "Thunderbolt security levels" as a primary > means of "security" against DMA attacks. This mean that users would need to > ack any device plugged in via userspace. In ~2018 machines started to use > the IOMMU for protection, but instead of dropping security levels a > convoluted flow was introduced: > * User hotplugs device > * Driver discovers supported tunnels > * Driver emits a uevent to userspace that a PCIe tunnel is present > * Userspace reads 'iommu_dma_protection' attribute (which currently > indicates an Intel IOMMU is present and was enabled pre-boot not that > it's active "now") > * Based on that value userspace then authorizes automatically or prompts > the user like how security level based support worked. There are legitimate reasons to disable PCIe tunneling even if the IOMMU bits are in place. The ACPI _OSC allows the boot firmware to do so and our "security levels" allows the userspace policy to do the same. I would not like to change that unless absolutely necessary.
