cd8b915ed9
- 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
250 lines
7 KiB
C
Executable file
250 lines
7 KiB
C
Executable file
/* This file contains a simple exception handler. Exceptions in user
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* processes are converted to signals. Exceptions in a kernel task cause
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* a panic.
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*/
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#include "../../kernel.h"
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#include "proto.h"
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#include <signal.h>
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#include <stdio.h>
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#include <string.h>
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#include <minix/sysutil.h>
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#include "../../proc.h"
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#include "../../proto.h"
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#include "../../vm.h"
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extern int vm_copy_in_progress, catch_pagefaults;
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extern struct proc *vm_copy_from, *vm_copy_to;
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void pagefault(vir_bytes old_eip, struct proc *pr, int trap_errno,
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u32_t *old_eipptr, u32_t *old_eaxptr, u32_t pagefaultcr2)
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{
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int s;
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vir_bytes ph;
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u32_t pte;
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int procok = 0, pcok = 0, rangeok = 0;
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int in_physcopy = 0;
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vir_bytes test_eip;
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vmassert(old_eipptr);
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vmassert(old_eaxptr);
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vmassert(*old_eipptr == old_eip);
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vmassert(old_eipptr != &old_eip);
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#if 0
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printf("kernel: pagefault in pr %d, addr 0x%lx, his cr3 0x%lx, actual cr3 0x%lx\n",
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pr->p_endpoint, pagefaultcr2, pr->p_seg.p_cr3, read_cr3());
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#endif
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if(pr->p_seg.p_cr3) {
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vmassert(pr->p_seg.p_cr3 == read_cr3());
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}
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test_eip = k_reenter ? old_eip : pr->p_reg.pc;
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in_physcopy = (test_eip > (vir_bytes) phys_copy) &&
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(test_eip < (vir_bytes) phys_copy_fault);
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if((k_reenter || iskernelp(pr)) &&
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catch_pagefaults && in_physcopy) {
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#if 0
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printf("pf caught! addr 0x%lx\n", pagefaultcr2);
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#endif
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*old_eipptr = (u32_t) phys_copy_fault;
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*old_eaxptr = pagefaultcr2;
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return;
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}
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/* System processes that don't have their own page table can't
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* have page faults. VM does have its own page table but also
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* can't have page faults (because VM has to handle them).
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*/
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if(k_reenter || (pr->p_endpoint <= INIT_PROC_NR &&
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!(pr->p_misc_flags & MF_FULLVM)) || pr->p_endpoint == VM_PROC_NR) {
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/* Page fault we can't / don't want to
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* handle.
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*/
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kprintf("pagefault for process %d ('%s'), pc = 0x%x, addr = 0x%x, flags = 0x%x, k_reenter %d\n",
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pr->p_endpoint, pr->p_name, pr->p_reg.pc,
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pagefaultcr2, trap_errno, k_reenter);
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proc_stacktrace(pr);
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minix_panic("page fault in system process", pr->p_endpoint);
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return;
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}
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/* Don't schedule this process until pagefault is handled. */
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vmassert(pr->p_seg.p_cr3 == read_cr3());
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vmassert(!RTS_ISSET(pr, PAGEFAULT));
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RTS_LOCK_SET(pr, PAGEFAULT);
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/* Save pagefault details, suspend process,
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* add process to pagefault chain,
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* and tell VM there is a pagefault to be
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* handled.
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*/
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pr->p_pagefault.pf_virtual = pagefaultcr2;
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pr->p_pagefault.pf_flags = trap_errno;
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pr->p_nextpagefault = pagefaults;
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pagefaults = pr;
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mini_notify(proc_addr(HARDWARE), VM_PROC_NR);
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return;
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}
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/*===========================================================================*
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* exception *
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*===========================================================================*/
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PUBLIC void exception(vec_nr, trap_errno, old_eip, old_cs, old_eflags,
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old_eipptr, old_eaxptr, pagefaultcr2)
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unsigned vec_nr;
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u32_t trap_errno;
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u32_t old_eip;
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U16_t old_cs;
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u32_t old_eflags;
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u32_t *old_eipptr;
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u32_t *old_eaxptr;
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u32_t pagefaultcr2;
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{
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/* An exception or unexpected interrupt has occurred. */
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struct proc *t;
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struct ex_s {
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char *msg;
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int signum;
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int minprocessor;
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};
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static struct ex_s ex_data[] = {
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{ "Divide error", SIGFPE, 86 },
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{ "Debug exception", SIGTRAP, 86 },
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{ "Nonmaskable interrupt", SIGBUS, 86 },
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{ "Breakpoint", SIGEMT, 86 },
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{ "Overflow", SIGFPE, 86 },
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{ "Bounds check", SIGFPE, 186 },
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{ "Invalid opcode", SIGILL, 186 },
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{ "Coprocessor not available", SIGFPE, 186 },
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{ "Double fault", SIGBUS, 286 },
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{ "Copressor segment overrun", SIGSEGV, 286 },
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{ "Invalid TSS", SIGSEGV, 286 },
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{ "Segment not present", SIGSEGV, 286 },
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{ "Stack exception", SIGSEGV, 286 }, /* STACK_FAULT already used */
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{ "General protection", SIGSEGV, 286 },
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{ "Page fault", SIGSEGV, 386 }, /* not close */
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{ NIL_PTR, SIGILL, 0 }, /* probably software trap */
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{ "Coprocessor error", SIGFPE, 386 },
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};
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register struct ex_s *ep;
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struct proc *saved_proc;
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if(k_reenter > 2) {
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/* This can't end well. */
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minix_panic("exception: k_reenter too high", k_reenter);
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}
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/* Save proc_ptr, because it may be changed by debug statements. */
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saved_proc = proc_ptr;
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ep = &ex_data[vec_nr];
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if (vec_nr == 2) { /* spurious NMI on some machines */
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kprintf("got spurious NMI\n");
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return;
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}
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if(vec_nr == PAGE_FAULT_VECTOR) {
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pagefault(old_eip, saved_proc, trap_errno,
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old_eipptr, old_eaxptr, pagefaultcr2);
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return;
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}
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/* If an exception occurs while running a process, the k_reenter variable
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* will be zero. Exceptions in interrupt handlers or system traps will make
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* k_reenter larger than zero.
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*/
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if (k_reenter == 0 && ! iskernelp(saved_proc)) {
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{
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kprintf(
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"vec_nr= %d, trap_errno= 0x%lx, eip= 0x%lx, cs= 0x%x, eflags= 0x%lx\n",
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vec_nr, (unsigned long)trap_errno,
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(unsigned long)old_eip, old_cs,
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(unsigned long)old_eflags);
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printseg("cs: ", 1, saved_proc, old_cs);
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printseg("ds: ", 0, saved_proc, saved_proc->p_reg.ds);
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if(saved_proc->p_reg.ds != saved_proc->p_reg.ss) {
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printseg("ss: ", 0, saved_proc, saved_proc->p_reg.ss);
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}
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proc_stacktrace(saved_proc);
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}
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cause_sig(proc_nr(saved_proc), ep->signum);
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return;
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}
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/* Exception in system code. This is not supposed to happen. */
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if (ep->msg == NIL_PTR || machine.processor < ep->minprocessor)
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kprintf("\nIntel-reserved exception %d\n", vec_nr);
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else
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kprintf("\n%s\n", ep->msg);
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kprintf("k_reenter = %d ", k_reenter);
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kprintf("vec_nr= %d, trap_errno= 0x%x, eip= 0x%x, cs= 0x%x, eflags= 0x%x\n",
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vec_nr, trap_errno, old_eip, old_cs, old_eflags);
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/* TODO should we enable this only when compiled for some debug mode? */
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if (saved_proc) {
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kprintf("scheduled was: process %d (%s), ", proc_nr(saved_proc), saved_proc->p_name);
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kprintf("pc = %u:0x%x\n", (unsigned) saved_proc->p_reg.cs,
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(unsigned) saved_proc->p_reg.pc);
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proc_stacktrace(saved_proc);
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minix_panic("exception in a kernel task", saved_proc->p_endpoint);
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}
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else {
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/* in an early stage of boot process we don't have processes yet */
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minix_panic("exception in kernel while booting", NO_NUM);
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}
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}
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/*===========================================================================*
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* stacktrace *
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*===========================================================================*/
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PUBLIC void proc_stacktrace(struct proc *whichproc)
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{
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reg_t bp, v_bp, v_pc, v_hbp;
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int iskernel;
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v_bp = whichproc->p_reg.fp;
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iskernel = iskernelp(whichproc);
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kprintf("%-8.8s %6d 0x%lx ",
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whichproc->p_name, whichproc->p_endpoint, whichproc->p_reg.pc);
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while(v_bp) {
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#define PRCOPY(pr, pv, v, n) \
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(iskernel ? (memcpy((char *) v, (char *) pv, n), OK) : \
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data_copy(pr->p_endpoint, pv, SYSTEM, (vir_bytes) (v), n))
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if(PRCOPY(whichproc, v_bp, &v_hbp, sizeof(v_hbp)) != OK) {
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kprintf("(v_bp 0x%lx ?)", v_bp);
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break;
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}
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if(PRCOPY(whichproc, v_bp + sizeof(v_pc), &v_pc, sizeof(v_pc)) != OK) {
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kprintf("(v_pc 0x%lx ?)", v_bp + sizeof(v_pc));
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break;
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}
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kprintf("0x%lx ", (unsigned long) v_pc);
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if(v_hbp != 0 && v_hbp <= v_bp) {
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kprintf("(hbp %lx ?)", v_hbp);
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break;
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}
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v_bp = v_hbp;
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}
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kprintf("\n");
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}
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