From: Jack Lange <jarusl@cs.northwestern.edu>
Date: Tue, 11 Aug 2009 21:47:28 +0000 (-0500)
Subject: minor changes to yields to avoid guest lock ups due to irq flooding scenarios
X-Git-Url: http://v3vee.org/palacios/gitweb/gitweb.cgi?p=palacios.git;a=commitdiff_plain;h=afffedf9ab57494864f0710a2530958fa9e216cc;hp=13fb068168e2826db39a481cf85033bb0156d2f9

minor changes to yields to avoid guest lock ups due to irq flooding scenarios
---

diff --git a/palacios/src/palacios/svm.c b/palacios/src/palacios/svm.c
index 5fadae1..d2444ac 100644
--- a/palacios/src/palacios/svm.c
+++ b/palacios/src/palacios/svm.c
@@ -293,7 +293,6 @@ static int start_svm_guest(struct guest_info *info) {
 	*/
 
 	// disable global interrupts for vm state transition
-
 	v3_clgi();
 
 
@@ -311,6 +310,11 @@ static int start_svm_guest(struct guest_info *info) {
 	// reenable global interrupts after vm exit
 	v3_stgi();
 
+
+	// Conditionally yield the CPU if the timeslice has expired
+	v3_yield_cond(info);
+
+
 	v3_update_time(info, tmp_tsc - info->time_state.cached_host_tsc);
 	num_exits++;
 	
@@ -322,10 +326,6 @@ static int start_svm_guest(struct guest_info *info) {
 	    }
 	}
 
-     
-	// Conditionally yield the CPU if the timeslice has expired
-	v3_yield_cond(info);
-
 	if (v3_handle_svm_exit(info) != 0) {
 	    vmcb_ctrl_t * guest_ctrl = GET_VMCB_CTRL_AREA((vmcb_t*)(info->vmm_data));
 	    addr_t host_addr;
diff --git a/palacios/src/palacios/svm_halt.c b/palacios/src/palacios/svm_halt.c
index 16239e8..2e6f9e2 100644
--- a/palacios/src/palacios/svm_halt.c
+++ b/palacios/src/palacios/svm_halt.c
@@ -30,7 +30,7 @@
 
 
 //
-// This should trigger a #GP if cpl!=0, otherwise, yield to host
+// This should trigger a #GP if cpl != 0, otherwise, yield to host
 //
 
 int v3_handle_svm_halt(struct guest_info * info) {
@@ -39,8 +39,8 @@ int v3_handle_svm_halt(struct guest_info * info) {
 	v3_raise_exception(info, GPF_EXCEPTION);
     } else {
     
-	ullong_t yield_start = 0;
-	ullong_t yield_stop = 0;
+	uint64_t yield_start = 0;
+	uint64_t yield_stop = 0;
 	uint32_t gap = 0;
 	
 	PrintDebug("CPU Yield\n");
@@ -53,7 +53,18 @@ int v3_handle_svm_halt(struct guest_info * info) {
 	//v3_update_time(info, yield_stop - yield_start);
 	gap = yield_stop - yield_start;
 
-	v3_raise_irq(info, 0);
+	/*  WARNING!!! WARNING!!!
+	 *  
+	 * DO NOT REMOVE THIS CONDITIONAL!!!
+	 *
+	 * It is common for an OS to issue an IO op, and then sit in a halt loop
+	 * waiting for the device to complete and raise an irq.
+	 * If you remove this then the timer interrupt will ALWAYS subvert the completion 
+	 * interrupt and stall the guest.
+	 */
+	if (!v3_intr_pending(info)) {
+	    v3_raise_irq(info, 0);
+	}
 
 	
 	PrintDebug("CPU Yield Done (%d cycles)\n", gap);