On Sat, 2006-04-01 at 10:30 +0100, Keir Fraser wrote:
> On 1 Apr 2006, at 04:55, Jimi Xenidis wrote:
>
> >> Before going down this route, what about just casting the field to
> >> long, since it is actually aligned on a suitable boundary, as it
> >> happens?
> >
> > We tried that, but to get the right bit we would have to use 56 not 0.
>
> Actually, evtchn_upcall_pending is touched in very few places in Xen
> common code. Using bit 56 is not very pretty but should be easy to hide
> behind a macro? You can hide the cast to long inside the same macro.
> You already need to arch-dep the event_pending() macro, for your MSR.EE
> check, and that's one of the main ways in which common code accesses
> the pending flag.
For reference, here's the PPC implementation:
/* HACK: evtchn_upcall_pending is only a byte, but our atomic instructions only
* store in 4/8 byte quantities. However, because evtchn_upcall_pending is part
* of the guest ABI, we can't change its size without breaking backwards
* compatibility. In this particular case, struct vcpu_info is big enough that
* we can safely store a full long into it. However, note that bit 0 of that
* byte is bit 56 when cast to a long.
*/
static inline int evtchn_test_and_set_pending(struct vcpu *v)
{
unsigned long *l = (unsigned long *)&v->vcpu_info->evtchn_upcall_pending;
return test_and_set_bit(56, l);
}
You'll notice I added an alignment attribute to that field because it
really really needs to be aligned for us. This has only been
build-tested on x86!
If it's acceptable, please apply.
Hide evtchn_upcall_pending test-and-set accesses behind a wrapper.
Signed-off-by: Hollis Blanchard <hollisb@xxxxxxxxxx>
diff -r aa088739693a xen/common/event_channel.c
--- a/xen/common/event_channel.c Tue Jun 13 10:48:08 2006 -0500
+++ b/xen/common/event_channel.c Tue Jun 13 14:52:05 2006 -0500
@@ -494,7 +494,7 @@ void evtchn_set_pending(struct vcpu *v,
if ( !test_bit (port, s->evtchn_mask) &&
!test_and_set_bit(port / BITS_PER_LONG,
&v->vcpu_info->evtchn_pending_sel) &&
- !test_and_set_bit(0, &v->vcpu_info->evtchn_upcall_pending) )
+ !evtchn_test_and_set_pending(v) )
{
evtchn_notify(v);
}
@@ -683,7 +683,7 @@ static long evtchn_unmask(evtchn_unmask_
test_bit (port, s->evtchn_pending) &&
!test_and_set_bit (port / BITS_PER_LONG,
&v->vcpu_info->evtchn_pending_sel) &&
- !test_and_set_bit (0, &v->vcpu_info->evtchn_upcall_pending) )
+ !evtchn_test_and_set_pending(v) )
{
evtchn_notify(v);
}
diff -r aa088739693a xen/include/asm-ia64/event.h
--- a/xen/include/asm-ia64/event.h Tue Jun 13 10:48:08 2006 -0500
+++ b/xen/include/asm-ia64/event.h Tue Jun 13 14:52:05 2006 -0500
@@ -74,4 +74,9 @@ static inline int arch_virq_is_global(in
return rc;
}
+static inline int evtchn_test_and_set_pending(struct vcpu *v)
+{
+ return test_and_set_bit(0, &v->vcpu_info->evtchn_upcall_pending);
+}
+
#endif
diff -r aa088739693a xen/include/asm-x86/event.h
--- a/xen/include/asm-x86/event.h Tue Jun 13 10:48:08 2006 -0500
+++ b/xen/include/asm-x86/event.h Tue Jun 13 14:52:05 2006 -0500
@@ -55,4 +55,9 @@ static inline int arch_virq_is_global(in
return 1;
}
+static inline int evtchn_test_and_set_pending(struct vcpu *v)
+{
+ return test_and_set_bit(0, &v->vcpu_info->evtchn_upcall_pending);
+}
+
#endif
diff -r aa088739693a xen/include/public/xen.h
--- a/xen/include/public/xen.h Tue Jun 13 10:48:08 2006 -0500
+++ b/xen/include/public/xen.h Tue Jun 13 14:52:05 2006 -0500
@@ -363,7 +363,7 @@ struct vcpu_info {
* an upcall activation. The mask is cleared when the VCPU requests
* to block: this avoids wakeup-waiting races.
*/
- uint8_t evtchn_upcall_pending;
+ uint8_t evtchn_upcall_pending __attribute__((aligned(sizeof(long))));
uint8_t evtchn_upcall_mask;
unsigned long evtchn_pending_sel;
struct arch_vcpu_info arch;
--
Hollis Blanchard
IBM Linux Technology Center
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