[Xen-changelog] [xen stable-4.8] xen: Fix determining when domain creation is complete

[patchbot@xxxxxxx]

commit 297cf3d1cf998d2fbc8e63e92034ce08f60c3b60
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Wed Jan 18 09:43:47 2017 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Wed Jan 18 09:43:47 2017 +0100

    xen: Fix determining when domain creation is complete
    
    d->creation_finished is used in several places alter behaviour depending on
    whether the domain is being created, or is already running.
    
    However, there is a latent bug if a toolstack component makes a pair of
    pause/unpause calls, where creation will be considered finished prematurely.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    Tested-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
    master commit: 9d71e02e8420b5d4a48d92446a1edbff498ee1c6
    master date: 2016-12-13 09:58:33 +0000
---
 xen/common/domain.c | 21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/xen/common/domain.c b/xen/common/domain.c
index 3abaca9..05130e2 100644
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -1004,13 +1004,6 @@ int domain_unpause_by_systemcontroller(struct domain *d)
 {
     int old, new, prev = d->controller_pause_count;
 
-    /*
-     * We record this information here for populate_physmap to figure out
-     * that the domain has finished being created. In fact, we're only
-     * allowed to set the MEMF_no_tlbflush flag during VM creation.
-     */
-    d->creation_finished = true;
-
     do
     {
         old = prev;
@@ -1022,6 +1015,20 @@ int domain_unpause_by_systemcontroller(struct domain *d)
         prev = cmpxchg(&d->controller_pause_count, old, new);
     } while ( prev != old );
 
+    /*
+     * d->controller_pause_count is initialised to 1, and the toolstack is
+     * responsible for making one unpause hypercall when it wishes the guest
+     * to start running.
+     *
+     * All other toolstack operations should make a pair of pause/unpause
+     * calls and rely on the reference counting here.
+     *
+     * Creation is considered finished when the controller reference count
+     * first drops to 0.
+     */
+    if ( new == 0 )
+        d->creation_finished = true;
+
     domain_unpause(d);
 
     return 0;
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.8

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