Hallo, this is about 'NKPT' definition, 'kernel_map' submaps, and 'vm_map_findspace' function.
Variable 'kernel_map' is used to manage kernel virtual address space. When 'vm_map_findspace' function deals with 'kernel_map' then 'pmap_growkernel' function is called. At least in 'i386' architecture, pmap implementation uses 'pmap_growkernel' function to allocate missing page tables. Missing page tables are problem, because no one checks 'pte' pointer for validity after use of 'vtopte' macro. 'NKPT' definition defines a number of preallocated page tables during system boot. Beyond 'kernel_map', some submaps of 'kernel_map' (buffer_map, pager_map,...) exist as result of 'kmem_suballoc' function call. When this submaps are used (for example 'kmem_alloc_nofault' function) and its virtual address subspace is at the end of used kernel virtual address space at the moment (and above 'NKPT' preallocation), then missing page tables are not allocated and double fault can happen. I have met this scenario and solved it by increasing page tables preallocation count ('NKPT' definition). It's temporary solution which works for the present. Can someone more advanced and sacred in virtual memory module solve it (in 'vm_map_findspace' function for example)? Or tell me that the problem is elsewhere... Thanks, Svata -- View this message in context: http://old.nabble.com/page-table-fault%2C-which-should-map-kernel-virtual-address-space-tp29760054p29760054.html Sent from the freebsd-hackers mailing list archive at Nabble.com. _______________________________________________ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "freebsd-hackers-unsubscr...@freebsd.org"