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LCA: Andrew Tanenbaum on creating reliable systemsLCA: Andrew Tanenbaum on creating reliable systemsPosted Jan 18, 2007 17:52 UTC (Thu) by JoeBuck (subscriber, #2330)In reply to: LCA: Andrew Tanenbaum on creating reliable systems by elanthis Parent article: LCA: Andrew Tanenbaum on creating reliable systems But the X server (at least large parts of it) is like an extended kernel. It runs as root, accesses the hardware directly, without going through the kernel, so bugs have the same ability to toast your system as the kernel does.
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LCA: Andrew Tanenbaum on creating reliable systems Posted Jan 18, 2007 20:54 UTC (Thu) by jamesh (guest, #1159) [Link] Well, the Minix setup basically required all IO port access to go through the kernel, and the policies for each daemon would say what it was allowed to access.
As for intelligent hardware like a modern GPU that can DMA to arbitrary memory locations, his solution was to use the IOMMU to limit where the device could write to. It wasn't clear whether they've implemented use of the IOMMU like this yet.
I've got no idea what impact this would have on performance of graphics operations.
LCA: Andrew Tanenbaum on creating reliable systems Posted Jan 18, 2007 22:42 UTC (Thu) by nix (subscriber, #2304) [Link] So Minix I/O port access always involves at least two ring transitions*per port I/O*?
Given the timing-sensitive nature of much port I/O that strikes me as both
LCA: Andrew Tanenbaum on creating reliable systems Posted Jan 24, 2007 14:01 UTC (Wed) by kleptog (subscriber, #1183) [Link] On i386 hardware, it's possible to grant an unprivelidged processes access to particular I/O ports, without having to do any ring transitions. On Linux it's the ioperm() function call.
These days people use memory-mapped I/O so mmap() is what you mostly need.
LCA: Andrew Tanenbaum on creating reliable systems Posted Feb 2, 2007 13:46 UTC (Fri) by willy (subscriber, #9762) [Link] Yes, but minix explicitly doesn't do ioperm, it really does call down to the microkernel to do IO port accesses. He talked about how 'evil' mmaped IO was.
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