[Xen-devel] [PATCH] x86/hvm: don't create a default ioreq server...

[Paul Durrant <paul.durrant@xxxxxxxxxx>]

...if the domain is not under construction.

If upstream QEMU is in use then it will explicitly create an ioreq server
rather than implicitly creating the default ioreq server, which is a
side-effect of reading HVM_PARAM_IOREQ_PFN, HVM_PARAM_BUFIOREQ_PFN,
or HVM_PARAM_BUFIOREQ_EVTCHN (as is done by legacy QEMUs).

However, if the domain is subsequently saved/migrated then those parameters
are read and hence the default server will be unnecessarily instantiated.

This patch adds an extra check of the 'creation_finished' flag when those
HVM params are read and will only instantiate the server if the domain is
under construction, which will always be the case when QEMU is invoked.

Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
---
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 xen/arch/x86/hvm/hvm.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index e0f936b..c531f37 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -5337,7 +5337,16 @@ static int hvmop_get_param(
     {
         domid_t domid;
 
-        /* May need to create server. */
+        /*
+         * It may be necessary to create a default ioreq server here,
+         * because legacy versions of QEMU are not aware of the new API
+         * for explicit ioreq server creation. However, if the domain
+         * is not under construction then it will not be QEMU querying
+         * the parameters and thus the query should have that side-effect.
+         */
+        if ( d->creation_finished )
+            break;
+
         domid = d->arch.hvm_domain.params[HVM_PARAM_DM_DOMAIN];
         rc = hvm_create_ioreq_server(d, domid, 1,
                                      HVM_IOREQSRV_BUFIOREQ_LEGACY, NULL);
-- 
2.1.4


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