Merge branch 'x86/urgent' into x86/asm to pick up dependent fixes

Signed-off-by: Ingo Molnar <mingo@kernel.org>

drivers/lguest/interrupts_and_traps.c

@@ -331,7 +331,7 @@ void set_interrupt(struct lg_cpu *cpu, unsigned int irq)
  * Actually now I think of it, it's possible that Ron *is* half the Plan 9
  * userbase.  Oh well.
  */
-static bool could_be_syscall(unsigned int num)
+bool could_be_syscall(unsigned int num)
 {
 	/* Normal Linux IA32_SYSCALL_VECTOR or reserved vector? */
 	return num == IA32_SYSCALL_VECTOR || num == syscall_vector;
@@ -416,6 +416,10 @@ bool deliver_trap(struct lg_cpu *cpu, unsigned int num)
  *
  * This routine indicates if a particular trap number could be delivered
  * directly.
+ *
+ * Unfortunately, Linux 4.6 started using an interrupt gate instead of a
+ * trap gate for syscalls, so this trick is ineffective.  See Mastery for
+ * how we could do this anyway...
  */
 static bool direct_trap(unsigned int num)
 {

drivers/lguest/lg.h

@@ -167,6 +167,7 @@ void guest_set_clockevent(struct lg_cpu *cpu, unsigned long delta);
 bool send_notify_to_eventfd(struct lg_cpu *cpu);
 void init_clockdev(struct lg_cpu *cpu);
 bool check_syscall_vector(struct lguest *lg);
+bool could_be_syscall(unsigned int num);
 int init_interrupts(void);
 void free_interrupts(void);
 

drivers/lguest/x86/core.c

@@ -429,8 +429,12 @@ void lguest_arch_handle_trap(struct lg_cpu *cpu)
 			return;
 		break;
 	case 32 ... 255:
+		/* This might be a syscall. */
+		if (could_be_syscall(cpu->regs->trapnum))
+			break;
+
 		/*
-		 * These values mean a real interrupt occurred, in which case
+		 * Other values mean a real interrupt occurred, in which case
 		 * the Host handler has already been run. We just do a
 		 * friendly check if another process should now be run, then
 		 * return to run the Guest again.