* evtchn_do_upcall() barrier between upcall_pending and pending_sel
@ 2008-05-08 10:18 Samuel Thibault
2008-05-08 10:25 ` Keir Fraser
0 siblings, 1 reply; 3+ messages in thread
From: Samuel Thibault @ 2008-05-08 10:18 UTC (permalink / raw
To: xen-devel
Hello,
In evtchn_do_upcall() there is a barrier between setting upcall_pending
and pending_sel, which makes sense to avoid losing events, however I
don't understand why it is a rmb(). memory-barriers.txt says that rmb()
only provides ordering of reads, not stores. Shouldn't that be a wmb()
instead then?
Samuel
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: evtchn_do_upcall() barrier between upcall_pending and pending_sel
2008-05-08 10:18 evtchn_do_upcall() barrier between upcall_pending and pending_sel Samuel Thibault
@ 2008-05-08 10:25 ` Keir Fraser
2008-05-08 10:34 ` Samuel Thibault
0 siblings, 1 reply; 3+ messages in thread
From: Keir Fraser @ 2008-05-08 10:25 UTC (permalink / raw
To: Samuel Thibault, xen-devel
Makes sense, yes.
-- Keir
On 8/5/08 11:18, "Samuel Thibault" <samuel.thibault@eu.citrix.com> wrote:
> Hello,
>
> In evtchn_do_upcall() there is a barrier between setting upcall_pending
> and pending_sel, which makes sense to avoid losing events, however I
> don't understand why it is a rmb(). memory-barriers.txt says that rmb()
> only provides ordering of reads, not stores. Shouldn't that be a wmb()
> instead then?
>
> Samuel
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: evtchn_do_upcall() barrier between upcall_pending and pending_sel
2008-05-08 10:25 ` Keir Fraser
@ 2008-05-08 10:34 ` Samuel Thibault
0 siblings, 0 replies; 3+ messages in thread
From: Samuel Thibault @ 2008-05-08 10:34 UTC (permalink / raw
To: Keir Fraser; +Cc: xen-devel
Keir Fraser, le Thu 08 May 2008 11:25:59 +0100, a écrit :
> Makes sense, yes.
Here are fixes then.
evtchn: Use wmb instead of rmb to enforce ordering between
evtchn_upcall_pending and evtchn_pending_sel stores.
Signed-off-by: Samuel Thibault <samuel.thibault@eu.citrix.com>
diff -r e39cf97647af drivers/xen/core/evtchn.c
--- a/drivers/xen/core/evtchn.c Mon May 05 10:17:41 2008 +0100
+++ b/drivers/xen/core/evtchn.c Thu May 08 11:33:59 2008 +0100
@@ -246,7 +246,7 @@ asmlinkage void evtchn_do_upcall(struct
#ifndef CONFIG_X86 /* No need for a barrier -- XCHG is a barrier on x86. */
/* Clear master flag /before/ clearing selector flag. */
- rmb();
+ wmb();
#endif
l1 = xchg(&vcpu_info->evtchn_pending_sel, 0);
minios: in non-x86 case, use wmb to enforce ordering between
evtchn_upcall_pending and evtchn_pending_sel stores.
Signed-off-by: Samuel Thibault <samuel.thibault@eu.citrix.com>
diff -r 4965e711fee8 extras/mini-os/hypervisor.c
--- a/extras/mini-os/hypervisor.c Wed May 07 15:36:32 2008 +0100
+++ b/extras/mini-os/hypervisor.c Thu May 08 11:31:35 2008 +0100
@@ -46,7 +46,11 @@ void do_hypervisor_callback(struct pt_re
in_callback = 1;
vcpu_info->evtchn_upcall_pending = 0;
- /* NB. No need for a barrier here -- XCHG is a barrier on x86. */
+ /* NB x86. No need for a barrier here -- XCHG is a barrier on x86. */
+#if !defined(__i386__) && !defined(__x86_64__)
+ /* clear master flag /before/ clearing selector flag. */
+ wmb();
+#endif
l1 = xchg(&vcpu_info->evtchn_pending_sel, 0);
while ( l1 != 0 )
{
^ permalink raw reply [flat|nested] 3+ messages in thread
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