Introduce "hcall" pointer to indicate pending hypercall.

Currently we look at the "trapnum" to see if the Guest wants a
hypercall.  But once the hypercall is done we have to reset trapnum to
a bogus value, otherwise if we exit to userspace and return, we'd run
the same hypercall twice (that was a nasty bug to find!).

This has two main effects:

1) When Jes's patch changes the hypercall args to be a generic "struct
   hcall_args" we simply change the type of "lg->hcall".  It's set by
   arch code, so if it has to copy args or something it can do so, and
   point "hcall" into lg->arch somewhere.

2) Async hypercalls only get run when an actual hypercall is pending.
   This simplfies the code a little and is a more logical semantic.

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

1 files changed, 7 insertions, 6 deletions

diff --git a/drivers/lguest/x86/core.c b/drivers/lguest/x86/core.c
index e2f46b16ce31..0cc251cbc72a 100644
--- a/drivers/lguest/x86/core.c
+++ b/drivers/lguest/x86/core.c
@@ -316,13 +316,14 @@ void lguest_arch_handle_trap(struct lguest *lg)
                         return;
                 break;
         case 32 ... 255:
-                /* These 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 fall through to loop
-                 * around: */
+                /* These 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 */
                 cond_resched();
-        case LGUEST_TRAP_ENTRY: /* Handled before re-entering Guest */
+                return;
+        case LGUEST_TRAP_ENTRY:
+                lg->hcall = lg->regs;
                 return;
         }