5ab8a4e764
needed to disable SVS at runtime. We set 'svs_enabled' to false, and hotpatch the kernel entry/exit points to eliminate the context switch code. We need to make sure there is no remote CPU that is executing the code we are hotpatching. So we use two barriers: * After the first one each CPU is guaranteed to be executing in svs_disable_cpu with interrupts disabled (this way it can't leave this place). * After the second one it is guaranteed that SVS is disabled, so we flush the cache, enable interrupts and continue execution normally. Between the two barriers, cpu0 will disable SVS (svs_enabled=false and hotpatch), and each CPU will restore the generic syscall entry point. Three notes: * We should call svs_pgg_update(true) afterwards, to put back PG_G on the kernel pages (for better performance). This will be done in another commit. * The fact that we disable interrupts does not prevent us from receiving an NMI, and it would be problematic. So we need to add some code to verify that PMCs are disabled before hotpatching. This will be done in another commit. * In svs_disable() we expect each CPU to be online. We need to add a check to make sure they indeed are. The sysctl allows only a 1->0 transition. There is no point in doing 0->1 transitions anyway, and it would be complicated to implement because we need to re-synchronize the CPU user page tables with the current ones (we lost track of them in the last 1->0 transition). |
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| common | ||
| compat | ||
| crypto | ||
| dist/pf | ||
| distrib | ||
| doc | ||
| etc | ||
| external | ||
| extsrc | ||
| games | ||
| include | ||
| lib | ||
| libexec | ||
| regress | ||
| rescue | ||
| sbin | ||
| share | ||
| sys | ||
| tests | ||
| tools | ||
| usr.bin | ||
| usr.sbin | ||
| build.sh | ||
| BUILDING | ||
| Makefile | ||
| Makefile.inc | ||
| UPDATING | ||