The XS_INTRODUCE command has two parameters: the mfn (or better: gfn)
of the domain's xenstore ring page and the event channel of the
domain for communicating with Xenstore.

The gfn is not really needed. It is stored in the per-domain struct
in xenstored and in case of another XS_INTRODUCE for the domain it
is tested to match the original value. If it doesn't match the
command is aborted via EINVAL, otherwise the event channel to the
domain is recreated.

As XS_INTRODUCE is limited to dom0 and there is no real downside of
recreating the event channel just omit the test for the gfn to
match and don't return EINVAL for multiple XS_INTRODUCE calls.

Signed-off-by: Juergen Gross <jgross@suse.com>
---
V2:
- remove mfn from struct domain (Julien Grall)
- replace mfn by gfn in comments (Julien Grall)

V3:
- allow multiple XS_INTRODUCE calls (Igor Druzhinin)
---
 tools/xenstore/xenstored_domain.c | 15 ++++-----------
 1 file changed, 4 insertions(+), 11 deletions(-)

diff --git a/tools/xenstore/xenstored_domain.c b/tools/xenstore/xenstored_domain.c
index 5858185211..06359503f0 100644
--- a/tools/xenstore/xenstored_domain.c
+++ b/tools/xenstore/xenstored_domain.c
@@ -55,10 +55,6 @@ struct domain
 	   repeated domain introductions. */
 	evtchn_port_t remote_port;
 
-	/* The mfn associated with the event channel, used only to validate
-	   repeated domain introductions. */
-	unsigned long mfn;
-
 	/* Domain path in store. */
 	char *path;
 
@@ -363,13 +359,12 @@ static void domain_conn_reset(struct domain *domain)
 	domain->interface->rsp_cons = domain->interface->rsp_prod = 0;
 }
 
-/* domid, mfn, evtchn, path */
+/* domid, gfn, evtchn, path */
 int do_introduce(struct connection *conn, struct buffered_data *in)
 {
 	struct domain *domain;
 	char *vec[3];
 	unsigned int domid;
-	unsigned long mfn;
 	evtchn_port_t port;
 	int rc;
 	struct xenstore_domain_interface *interface;
@@ -381,7 +376,7 @@ int do_introduce(struct connection *conn, struct buffered_data *in)
 		return EACCES;
 
 	domid = atoi(vec[0]);
-	mfn = atol(vec[1]);
+	/* Ignore the gfn, we don't need it. */
 	port = atoi(vec[2]);
 
 	/* Sanity check args. */
@@ -402,21 +397,19 @@ int do_introduce(struct connection *conn, struct buffered_data *in)
 			return rc;
 		}
 		domain->interface = interface;
-		domain->mfn = mfn;
 
 		/* Now domain belongs to its connection. */
 		talloc_steal(domain->conn, domain);
 
 		fire_watches(NULL, in, "@introduceDomain", false);
-	} else if ((domain->mfn == mfn) && (domain->conn != conn)) {
+	} else {
 		/* Use XS_INTRODUCE for recreating the xenbus event-channel. */
 		if (domain->port)
 			xenevtchn_unbind(xce_handle, domain->port);
 		rc = xenevtchn_bind_interdomain(xce_handle, domid, port);
 		domain->port = (rc == -1) ? 0 : rc;
 		domain->remote_port = port;
-	} else
-		return EINVAL;
+	}
 
 	domain_conn_reset(domain);
 
-- 
2.16.4

On Thu, Apr 30, 2020 at 07:38:42AM +0200, Juergen Gross wrote:
> The XS_INTRODUCE command has two parameters: the mfn (or better: gfn)
> of the domain's xenstore ring page and the event channel of the
> domain for communicating with Xenstore.
> 
> The gfn is not really needed. It is stored in the per-domain struct
> in xenstored and in case of another XS_INTRODUCE for the domain it
> is tested to match the original value. If it doesn't match the
> command is aborted via EINVAL, otherwise the event channel to the
> domain is recreated.
> 
> As XS_INTRODUCE is limited to dom0 and there is no real downside of
> recreating the event channel just omit the test for the gfn to
> match and don't return EINVAL for multiple XS_INTRODUCE calls.
> 
> Signed-off-by: Juergen Gross <jgross@suse.com>

Acked-by: Wei Liu <wl@xen.org>

Hi Juergen,

On 30/04/2020 06:38, Juergen Gross wrote:
> The XS_INTRODUCE command has two parameters: the mfn (or better: gfn)
> of the domain's xenstore ring page and the event channel of the
> domain for communicating with Xenstore.
> 
> The gfn is not really needed. It is stored in the per-domain struct
> in xenstored and in case of another XS_INTRODUCE for the domain it
> is tested to match the original value. If it doesn't match the
> command is aborted via EINVAL, otherwise the event channel to the
> domain is recreated.
> 
> As XS_INTRODUCE is limited to dom0 and there is no real downside of
> recreating the event channel just omit the test for the gfn to
> match and don't return EINVAL for multiple XS_INTRODUCE calls.
> 
> Signed-off-by: Juergen Gross <jgross@suse.com>

Reviewed-by: Julien Grall <jgrall@amazon.com>

Cheers,

-- 
Julien Grall