Please backport bee980d9e9642e96351fa3ca9077b853ecf62f57 (xen/events: Handle VIRQ_TIMER before any other hardirq in event loop.) to earlier kernels v3.8...and so on

index 74d77df..0f1d1ba 100644
@@ -1288,7 +1288,7 @@ static void __xen_evtchn_do_upcall(void)
 {
 	int start_word_idx, start_bit_idx;
 	int word_idx, bit_idx;
-	int i;
+	int i, irq;
 	int cpu = get_cpu();
 	struct shared_info *s = HYPERVISOR_shared_info;
 	struct vcpu_info *vcpu_info = __this_cpu_read(xen_vcpu);

@@ -1296,6 +1296,8 @@ static void __xen_evtchn_do_upcall(void)
 
 	do {
 		unsigned long pending_words;
+		unsigned long pending_bits;
+		struct irq_desc *desc;
 
 		vcpu_info->evtchn_upcall_pending = 0;
 

@@ -1306,6 +1308,17 @@ static void __xen_evtchn_do_upcall(void)
 		/* Clear master flag /before/ clearing selector flag. */
 		wmb();
 #endif
+		if ((irq = per_cpu(virq_to_irq, cpu)[VIRQ_TIMER]) != -1) {
+			int evtchn = evtchn_from_irq(irq);
+			word_idx = evtchn / BITS_PER_LONG;
+			pending_bits = evtchn % BITS_PER_LONG;
+			if (active_evtchns(cpu, s, word_idx) & (1ULL << pending_bits)) {
+				desc = irq_to_desc(irq);
+				if (desc)
+					generic_handle_irq_desc(irq, desc);
+			}
+		}
+
 		pending_words = xchg(&vcpu_info->evtchn_pending_sel, 0);
 
 		start_word_idx = __this_cpu_read(current_word_idx);

@@ -1314,7 +1327,6 @@ static void __xen_evtchn_do_upcall(void)
 		word_idx = start_word_idx;
 
 		for (i = 0; pending_words != 0; i++) {
-			unsigned long pending_bits;
 			unsigned long words;
 
 			words = MASK_LSBS(pending_words, word_idx);

@@ -1343,8 +1355,7 @@ static void __xen_evtchn_do_upcall(void)
 
 			do {
 				unsigned long bits;
-				int port, irq;
-				struct irq_desc *desc;
+				int port;
 
 				bits = MASK_LSBS(pending_bits, bit_idx);