lguest: suppress interrupts for single insn, not range.

The last patch reduced our interrupt-suppression region to one address,
so simplify the code somewhat.

Also, remove the obsolete undefined instruction ranges and the comment
which refers to lguest_guest.S instead of head_32.S.

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

3 files changed, 7 insertions, 8 deletions

diff --git a/drivers/lguest/hypercalls.c b/drivers/lguest/hypercalls.c
index 1219af493c0f..19a32280731d 100644
--- a/drivers/lguest/hypercalls.c
+++ b/drivers/lguest/hypercalls.c
@@ -211,10 +211,9 @@ static void initialize(struct lg_cpu *cpu)
 
         /*
          * The Guest tells us where we're not to deliver interrupts by putting
-         * the range of addresses into "struct lguest_data".
+         * the instruction address into "struct lguest_data".
          */
-        if (get_user(cpu->lg->noirq_start, &cpu->lg->lguest_data->noirq_start)
-            || get_user(cpu->lg->noirq_end, &cpu->lg->lguest_data->noirq_end))
+        if (get_user(cpu->lg->noirq_iret, &cpu->lg->lguest_data->noirq_iret))
                 kill_guest(cpu, "bad guest page %p", cpu->lg->lguest_data);
 
         /*
diff --git a/drivers/lguest/interrupts_and_traps.c b/drivers/lguest/interrupts_and_traps.c
index 70dfcdc29f1f..6d4c072b61e1 100644
--- a/drivers/lguest/interrupts_and_traps.c
+++ b/drivers/lguest/interrupts_and_traps.c
@@ -204,8 +204,7 @@ void try_deliver_interrupt(struct lg_cpu *cpu, unsigned int irq, bool more)
          * They may be in the middle of an iret, where they asked us never to
          * deliver interrupts.
          */
-        if (cpu->regs->eip >= cpu->lg->noirq_start &&
-           (cpu->regs->eip < cpu->lg->noirq_end))
+        if (cpu->regs->eip == cpu->lg->noirq_iret)
                 return;
 
         /* If they're halted, interrupts restart them. */
@@ -395,8 +394,9 @@ static bool direct_trap(unsigned int num)
  * The Guest has the ability to turn its interrupt gates into trap gates,
  * if it is careful.  The Host will let trap gates can go directly to the
  * Guest, but the Guest needs the interrupts atomically disabled for an
- * interrupt gate.  It can do this by pointing the trap gate at instructions
- * within noirq_start and noirq_end, where it can safely disable interrupts.
+ * interrupt gate.  The Host could provide a mechanism to register more
+ * "no-interrupt" regions, and the Guest could point the trap gate at
+ * instructions within that region, where it can safely disable interrupts.
  */
 
 /*M:006
diff --git a/drivers/lguest/lg.h b/drivers/lguest/lg.h
index 307e8b39e7d1..ac8ad0461e80 100644
--- a/drivers/lguest/lg.h
+++ b/drivers/lguest/lg.h
@@ -102,7 +102,7 @@ struct lguest {
 
         struct pgdir pgdirs[4];
 
-        unsigned long noirq_start, noirq_end;
+        unsigned long noirq_iret;
 
         unsigned int stack_pages;
         u32 tsc_khz;