Limit the maximum number of back-to-back iterations of a "rep; ins/outs"

to 16. This is arbitrary and is used to ensure that a vcpu goes back into
the vm_run() loop to process interrupts or rendezvous events in a timely
fashion.

Found with:	Coverity Scan
CID:		1216436

1 files changed, 11 insertions, 3 deletions

diff --git a/usr.sbin/bhyve/inout.c b/usr.sbin/bhyve/inout.c
index babd6e1..cb34b80 100644
--- a/usr.sbin/bhyve/inout.c
+++ b/usr.sbin/bhyve/inout.c
@@ -55,6 +55,10 @@ SET_DECLARE(inout_port_set, struct inout_port);
 #define	VERIFY_IOPORT(port, size) \
 	assert((port) >= 0 && (size) > 0 && ((port) + (size)) <= MAX_IOPORTS)
 
+#ifndef min
+#define	min(a, b)	((a) < (b) ? (a) : (b))
+#endif
+
 static struct {
 	const char	*name;
 	int		flags;
@@ -109,7 +113,7 @@ emulate_inout(struct vmctx *ctx, int vcpu, struct vm_exit *vmexit, int strict)
 	void *arg;
 	int error, retval;
 	enum vm_reg_name idxreg;
-	uint64_t gla, index, count;
+	uint64_t gla, index, iterations, count;
 	struct vm_inout_str *vis;
 	struct iovec iov[2];
 
@@ -151,14 +155,17 @@ emulate_inout(struct vmctx *ctx, int vcpu, struct vm_exit *vmexit, int strict)
 		/* Count register */
 		count = vis->count & vie_size2mask(addrsize);
 
-		while (count) {
+		/* Limit number of back-to-back in/out emulations to 16 */
+		iterations = min(count, 16);
+		while (iterations > 0) {
 			if (vie_calculate_gla(vis->paging.cpu_mode,
 			    vis->seg_name, &vis->seg_desc, index, bytes,
 			    addrsize, prot, &gla)) {
 				error = vm_inject_exception2(ctx, vcpu,
 				    IDT_GP, 0);
 				assert(error == 0);
-				return (INOUT_RESTART);
+				retval = INOUT_RESTART;
+				break;
 			}
 
 			error = vm_gla2gpa(ctx, vcpu, &vis->paging, gla, bytes,
@@ -196,6 +203,7 @@ emulate_inout(struct vmctx *ctx, int vcpu, struct vm_exit *vmexit, int strict)
 				index += bytes;
 
 			count--;
+			iterations--;
 		}
 
 		/* Update index register */