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This thread has gotten mixed up.. First this series as it is has nothing to do with RMRs. What the latter part is discussing is a future series to implement what I think MS calls "boot DMA security". Meaning we don't get into a position of allowing a device access to OS memory, even through ATS translated requests, until after userspace has approved the device. This is something that should combine with Dynamic Root of Trust for Measurement, as DRTM is much less useful if DMA can mutate the OS code after the DTRM returns. It is also meaningful for systems with encrypted PCI where the OS can measure the PCI device before permitting it access to anything. So... When we do implement this new security mode, what should it do if FW attempts to attack the kernel with these nonsensical RMR configurations? With DRTM we explicitly don't trust the FW for security anymore, so it is a problem. I strongly suspect the answer is that RMR has to be ignored in this more secure mode. > However I think there would be no point exposing the ATS details to > the VM to begin with. It's the host's decision to trust the device > to play in the translated PA space and system cache coherency > protocol, and no guest would be allowed to mess with those aspects > either way, so there seems no obvious good reason for them to know > at all. If the vSMMU is presented then the guest must be aware of the ATS because only the guest can generate the ATC invalidations for changes in the S1. Without a vSMMU the ATS can be hidden from the guest. Jason