Primary goal for these changes is:

- no longer have kernel have its own page table that is loaded
    on every kernel entry (trap, interrupt, exception). the primary
    purpose is to reduce the number of required reloads.
Result:
  - kernel can only access memory of process that was running when
    kernel was entered
  - kernel must be mapped into every process page table, so traps to
    kernel keep working
Problem:
  - kernel must often access memory of arbitrary processes (e.g. send
    arbitrary processes messages); this can't happen directly any more;
    usually because that process' page table isn't loaded at all, sometimes
    because that memory isn't mapped in at all, sometimes because it isn't
    mapped in read-write.
So:
  - kernel must be able to map in memory of any process, in its own
    address space.
Implementation:
  - VM and kernel share a range of memory in which addresses of
    all page tables of all processes are available. This has two purposes:
      . Kernel has to know what data to copy in order to map in a range
      . Kernel has to know where to write the data in order to map it in
    That last point is because kernel has to write in the currently loaded
    page table.
  - Processes and kernel are separated through segments; kernel segments
    haven't changed.
  - The kernel keeps the process whose page table is currently loaded
    in 'ptproc.'
  - If it wants to map in a range of memory, it writes the value of the
    page directory entry for that range into the page directory entry
    in the currently loaded map. There is a slot reserved for such
    purposes. The kernel can then access this memory directly.
  - In order to do this, its segment has been increased (and the
    segments of processes start where it ends).
  - In the pagefault handler, detect if the kernel is doing
    'trappable' memory access (i.e. a pagefault isn't a fatal
     error) and if so,
       - set the saved instruction pointer to phys_copy_fault,
	 breaking out of phys_copy
       - set the saved eax register to the address of the page
	 fault, both for sanity checking and for checking in
	 which of the two ranges that phys_copy was called
	 with the fault occured
  - Some boot-time processes do not have their own page table,
    and are mapped in with the kernel, and separated with
    segments. The kernel detects this using HASPT. If such a
    process has to be scheduled, any page table will work and
    no page table switch is done.

Major changes in kernel are
  - When accessing user processes memory, kernel no longer
    explicitly checks before it does so if that memory is OK.
    It simply makes the mapping (if necessary), tries to do the
    operation, and traps the pagefault if that memory isn't present;
    if that happens, the copy function returns EFAULT.
    So all of the CHECKRANGE_OR_SUSPEND macros are gone.
  - Kernel no longer has to copy/read and parse page tables.
  - A message copying optimisation: when messages are copied, and
    the recipient isn't mapped in, they are copied into a buffer
    in the kernel. This is done in QueueMess. The next time
    the recipient is scheduled, this message is copied into
    its memory. This happens in schedcheck().
    This eliminates the mapping/copying step for messages, and makes
    it easier to deliver messages. This eliminates soft_notify.
  - Kernel no longer creates a page table at all, so the vm_setbuf
    and pagetable writing in memory.c is gone.

Minor changes in kernel are
  - ipc_stats thrown out, wasn't used
  - misc flags all renamed to MF_*
  - NOREC_* macros to enter and leave functions that should not
    be called recursively; just sanity checks really
  - code to fully decode segment selectors and descriptors
    to print on exceptions
  - lots of vmassert()s added, only executed if DEBUG_VMASSERT is 1

kernel/glo.h

@@ -16,6 +16,7 @@
 #include <minix/config.h>
 #include <archtypes.h>
 #include "config.h"
+#include "debug.h"
 
 /* Variables relating to shutting down MINIX. */
 EXTERN char kernel_exception;		/* TRUE after system exceptions */
@@ -29,14 +30,13 @@ EXTERN struct k_randomness krandom;	/* gather kernel random information */
 EXTERN struct loadinfo kloadinfo;	/* status of load average */
 
 /* Process scheduling information and the kernel reentry count. */
-EXTERN struct proc *prev_ptr;	/* previously running process */
 EXTERN struct proc *proc_ptr;	/* pointer to currently running process */
 EXTERN struct proc *next_ptr;	/* next process to run after restart() */
+EXTERN struct proc *prev_ptr;	
 EXTERN struct proc *bill_ptr;	/* process to bill for clock ticks */
 EXTERN struct proc *vmrestart;  /* first process on vmrestart queue */
 EXTERN struct proc *vmrequest;  /* first process on vmrequest queue */
 EXTERN struct proc *pagefaults; /* first process on pagefault queue */
-EXTERN struct proc *softnotify;	/* first process on softnotify queue */
 EXTERN char k_reenter;		/* kernel reentry count (entry count less 1) */
 EXTERN unsigned lost_ticks;	/* clock ticks counted outside clock task */
 
@@ -47,32 +47,6 @@ EXTERN int irq_actids[NR_IRQ_VECTORS];		/* IRQ ID bits active */
 EXTERN int irq_use;				/* map of all in-use irq's */
 EXTERN u32_t system_hz;				/* HZ value */
 
-EXTERN struct ipc_stats
-{
-	unsigned long deadproc;
-	unsigned long bad_endpoint;
-	unsigned long dst_not_allowed;
-	unsigned long bad_call;
-	unsigned long call_not_allowed;
-	unsigned long bad_buffer;
-	unsigned long deadlock;
-	unsigned long not_ready;
-	unsigned long src_died;
-	unsigned long dst_died;
-	unsigned long no_priv;
-	unsigned long bad_size;
-	unsigned long bad_senda;
-	u64_t total;
-} ipc_stats;
-extern endpoint_t ipc_stats_target;
-
-EXTERN struct system_stats
-{
-	unsigned long bad_req;
-	unsigned long not_allowed;
-	u64_t total;
-} sys_stats;
-
 /* Miscellaneous. */
 EXTERN reg_t mon_ss, mon_sp;		/* boot monitor stack */
 EXTERN int mon_return;			/* true if we can return to monitor */
@@ -85,18 +59,14 @@ EXTERN char params_buffer[512];		/* boot monitor parameters */
 EXTERN int minix_panicing;
 EXTERN int locklevel;
 
-EXTERN unsigned long cr3switch;
-EXTERN unsigned long cr3reload;
+#if DEBUG_TRACE
+EXTERN int verboseflags;
+#endif
 
 /* VM */
-EXTERN phys_bytes vm_base;
-EXTERN phys_bytes vm_size;
-EXTERN phys_bytes vm_mem_high;
 EXTERN int vm_running;
-EXTERN int must_notify_vm;
-
-/* Verbose flags (debugging). */
-EXTERN int verbose_vm;
+EXTERN int catch_pagefaults;
+EXTERN struct proc *ptproc;
 
 /* Timing */
 EXTERN util_timingdata_t timingdata[TIMING_CATEGORIES];