On Tue, Nov 27, 2018 at 10:54:26AM +0200, Mika Westerberg wrote: > On Mon, Nov 26, 2018 at 06:17:11PM -0600, Bjorn Helgaas wrote: > > Hi Mika, > > Hi, > > > On Mon, Nov 26, 2018 at 02:15:23PM +0300, Mika Westerberg wrote: > > > Recent systems with Thunderbolt ports may support IOMMU natively. > > > > This sentence doesn't make sense to me. There's no logical connection > > between having an IOMMU and having a Thunderbolt port. > > > > > This means that the platform utilizes IOMMU to prevent DMA attacks > > > over externally exposed PCIe root ports (typically Thunderbolt > > > ports) > > > > Nor this one. The platform only uses the IOMMU to prevent DMA attacks > > if the OS chooses to do that. I think by "platform" you're referring to the system firmware; I was only thinking of the hardware, so the IOMMU wouldn't be used unless someone (the OS) enabled it. But your cover letter talks about the BIOS enabling some IOMMU functionality. > I guess I'm trying to say here that the recent changes add such support > to the platform BIOS that allows the OS to enable IOMMU without being > compromised by a malicious device that is already connected. The BIOS > sets the new ACPI DMAR bit in that case. Ah, there's useful info to this effect in your [0/4] cover letter. That info and the URL should be in the changelog of one of the patches so it doesn't get lost. > > > The system BIOS marks these PCIe root ports as being externally facing > > > ports by implementing following ACPI _DSD [1] under the root port in > > > question: > > > > There's no standard that requires this, so the best we can say is that > > a system BIOS *may* mark externally facing ports with this mechanism. > > There is no standard but I'm quite sure this is something that will be > required to be implemented properly by the OEM by Microsoft hardware > compatibility suite. Sure. Your statement suggests that all external ports will be marked with the _DSD. I'm just pointing out that the OS can't assume that because there are probably systems in the field that predate the _DSD. Bjorn
