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which takes an physical address instead of an virtual one, for loading TTEs of the kernel TSB so we no longer need to lock the kernel TSB into the dTLB, which only has a very limited number of lockable dTLB slots. The net result is that we now basically can handle a kernel TSB of any size and no longer need to limit the kernel address space based on the number of dTLB slots available for locked entries. Consequently, other parts of the trap handlers now also only access the the kernel TSB via its physical address in order to avoid nested traps, as does the PMAP bootstrap code as we haven't taken over the trap table at that point, yet. Apart from that the kernel TSB now is accessed via a direct mapping when we are otherwise taking advantage of ASI_ATOMIC_QUAD_LDD_PHYS so no further code changes are needed. Most of this is implemented by extending the patching of the TSB addresses and mask as well as the ASIs used to load it into the trap table so the runtime overhead of this change is rather low. Currently the use of ASI_ATOMIC_QUAD_LDD_PHYS is not yet enabled on SPARC64 CPUs due to lack of testing and due to the fact it might require minor adjustments there. Theoretically it should be possible to use the same approach also for the user TSB, which already is not locked into the dTLB, avoiding nested traps. However, for reasons I don't understand yet OpenSolaris only does that with SPARC64 CPUs. On the other hand I think that also addressing the user TSB physically and thus avoiding nested traps would get us closer to sharing this code with sun4v, which only supports trap level 0 and 1, so eventually we could have a single kernel which runs on both sun4u and sun4v (as does Linux and OpenBSD). Developed at and committed from: 27C3 |
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