common: make hypercall preemption checks consistent

- never preempt on the first iteration (ensure forward progress)
- do cheap checks first

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Tim Deegan <tim@xen.org>
Acked-by: Keir Fraser <keir@xen.org>

diff --git a/xen/common/memory.c b/xen/common/memory.c
index 9d0d32e326e2ccdb9bde092972a54d3eadc468f0..4d6ffeed95d1cd19e6b910b99dc6be75e6dc3ca9 100644 (file)
--- a/xen/common/memory.c
+++ b/xen/common/memory.c
@@ -63,7 +63,7 @@ static void increase_reservation(struct memop_args *a)
 
     for ( i = a->nr_done; i < a->nr_extents; i++ )
     {
-        if ( hypercall_preempt_check() )
+        if ( i != a->nr_done && hypercall_preempt_check() )
         {
             a->preempted = 1;
             goto out;
@@ -109,7 +109,7 @@ static void populate_physmap(struct memop_args *a)
 
     for ( i = a->nr_done; i < a->nr_extents; i++ )
     {
-        if ( hypercall_preempt_check() )
+        if ( i != a->nr_done && hypercall_preempt_check() )
         {
             a->preempted = 1;
             goto out;
@@ -268,7 +268,7 @@ static void decrease_reservation(struct memop_args *a)
 
     for ( i = a->nr_done; i < a->nr_extents; i++ )
     {
-        if ( hypercall_preempt_check() && i != a->nr_done )
+        if ( i != a->nr_done && hypercall_preempt_check() )
         {
             a->preempted = 1;
             goto out;
@@ -398,7 +398,8 @@ static long memory_exchange(XEN_GUEST_HANDLE_PARAM(xen_memory_exchange_t) arg)
           i < (exch.in.nr_extents >> in_chunk_order);
           i++ )
     {
-        if ( hypercall_preempt_check() )
+        if ( i != (exch.nr_exchanged >> in_chunk_order) &&
+             hypercall_preempt_check() )
         {
             exch.nr_exchanged = i << in_chunk_order;
             rcu_unlock_domain(d);

diff --git a/xen/common/multicall.c b/xen/common/multicall.c
index 2afba98d05fceec0695a315d01fe188b9798959a..e66c7982364e05ee516745d0a85b4b416ca80dd6 100644 (file)
--- a/xen/common/multicall.c
+++ b/xen/common/multicall.c
@@ -52,7 +52,7 @@ do_multicall(
 
     for ( i = 0; !rc && i < nr_calls; i++ )
     {
-        if ( hypercall_preempt_check() )
+        if ( i && hypercall_preempt_check() )
             goto preempted;
 
         if ( unlikely(__copy_from_guest(&mcs->call, call_list, 1)) )

diff --git a/xen/drivers/char/console.c b/xen/drivers/char/console.c
index 7d4383ce6ff9c5286b14f691abfd8985e012f3a7..beda79fd5d850b11dac6818c218d16ce1332562e 100644 (file)
--- a/xen/drivers/char/console.c
+++ b/xen/drivers/char/console.c
@@ -375,12 +375,12 @@ static DECLARE_SOFTIRQ_TASKLET(notify_dom0_con_ring_tasklet,
 static long guest_console_write(XEN_GUEST_HANDLE_PARAM(char) buffer, int count)
 {
     char kbuf[128];
-    int kcount;
+    int kcount = 0;
     struct domain *cd = current->domain;
 
     while ( count > 0 )
     {
-        if ( hypercall_preempt_check() )
+        if ( kcount && hypercall_preempt_check() )
             return hypercall_create_continuation(
                 __HYPERVISOR_console_io, "iih",
                 CONSOLEIO_write, count, buffer);