Make shadow IDT a complete IDT with 256 entries.

This simplifies the code a little, in preparation for allowing
alternate system call vectors in guests (Plan 9 uses 0x40).

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --git a/drivers/lguest/interrupts_and_traps.c b/drivers/lguest/interrupts_and_traps.c
index 3973123..0dfb090 100644 (file)
--- a/drivers/lguest/interrupts_and_traps.c
+++ b/drivers/lguest/interrupts_and_traps.c
@@ -218,10 +218,9 @@ int deliver_trap(struct lguest *lg, unsigned int num)
  * system calls down from 1750ns to 270ns.  Plus, if lguest didn't do it, all
  * the other hypervisors would tease it.
  *
- * This routine determines if a trap can be delivered directly. */
-static int direct_trap(const struct lguest *lg,
-                      const struct desc_struct *trap,
-                      unsigned int num)
+ * This routine indicates if a particular trap number could be delivered
+ * directly. */
+static int direct_trap(unsigned int num)
 {
        /* Hardware interrupts don't go to the Guest at all (except system
         * call). */
@@ -232,14 +231,7 @@ static int direct_trap(const struct lguest *lg,
         * fault address), general protection faults (in/out emulation) and
         * device not available (TS handling), and of course, the hypercall
         * trap. */
-       if (num == 14 || num == 13 || num == 7 || num == LGUEST_TRAP_ENTRY)
-               return 0;
-
-       /* Only trap gates (type 15) can go direct to the Guest.  Interrupt
-        * gates (type 14) disable interrupts as they are entered, which we
-        * never let the Guest do.  Not present entries (type 0x0) also can't
-        * go direct, of course 8) */
-       return idt_type(trap->a, trap->b) == 0xF;
+       return num != 14 && num != 13 && num != 7 && num != LGUEST_TRAP_ENTRY;
 }
 /*:*/
 
@@ -348,15 +340,11 @@ void load_guest_idt_entry(struct lguest *lg, unsigned int num, u32 lo, u32 hi)
         * to copy this again. */
        lg->changed |= CHANGED_IDT;
 
-       /* The IDT which we keep in "struct lguest" only contains 32 entries
-        * for the traps and LGUEST_IRQS (32) entries for interrupts.  We
-        * ignore attempts to set handlers for higher interrupt numbers, except
-        * for the system call "interrupt" at 128: we have a special IDT entry
-        * for that. */
-       if (num < ARRAY_SIZE(lg->idt))
+       /* Check that the Guest doesn't try to step outside the bounds. */
+       if (num >= ARRAY_SIZE(lg->idt))
+               kill_guest(lg, "Setting idt entry %u", num);
+       else
                set_trap(lg, &lg->idt[num], num, lo, hi);
-       else if (num == SYSCALL_VECTOR)
-               set_trap(lg, &lg->syscall_idt, num, lo, hi);
 }
 
 /* The default entry for each interrupt points into the Switcher routines which
@@ -399,20 +387,21 @@ void copy_traps(const struct lguest *lg, struct desc_struct *idt,
 
        /* We can simply copy the direct traps, otherwise we use the default
         * ones in the Switcher: they will return to the Host. */
-       for (i = 0; i < FIRST_EXTERNAL_VECTOR; i++) {
-               if (direct_trap(lg, &lg->idt[i], i))
+       for (i = 0; i < ARRAY_SIZE(lg->idt); i++) {
+               /* If no Guest can ever override this trap, leave it alone. */
+               if (!direct_trap(i))
+                       continue;
+
+               /* Only trap gates (type 15) can go direct to the Guest.
+                * Interrupt gates (type 14) disable interrupts as they are
+                * entered, which we never let the Guest do.  Not present
+                * entries (type 0x0) also can't go direct, of course. */
+               if (idt_type(lg->idt[i].a, lg->idt[i].b) == 0xF)
                        idt[i] = lg->idt[i];
                else
+                       /* Reset it to the default. */
                        default_idt_entry(&idt[i], i, def[i]);
        }
-
-       /* Don't forget the system call trap!  The IDT entries for other
-        * interupts never change, so no need to copy them. */
-       i = SYSCALL_VECTOR;
-       if (direct_trap(lg, &lg->syscall_idt, i))
-               idt[i] = lg->syscall_idt;
-       else
-               default_idt_entry(&idt[i], i, def[i]);
 }
 
 void guest_set_clockevent(struct lguest *lg, unsigned long delta)

diff --git a/drivers/lguest/lg.h b/drivers/lguest/lg.h
index c9d1dc2..c1ca127 100644 (file)
--- a/drivers/lguest/lg.h
+++ b/drivers/lguest/lg.h
@@ -184,8 +184,7 @@ struct lguest
        struct desc_struct gdt[GDT_ENTRIES];
 
        /* The IDT entries: some copied into lguest_ro_state when running. */
-       struct desc_struct idt[FIRST_EXTERNAL_VECTOR+LGUEST_IRQS];
-       struct desc_struct syscall_idt;
+       struct desc_struct idt[IDT_ENTRIES];
 
        /* Virtual clock device */
        struct hrtimer hrt;