xenbus: Allow PVH dom0 a non-local xenstore

Make xenbus_init() allow a non-local xenstore for a PVH dom0 - it is
currently forced to XS_LOCAL.  With Hyperlaunch booting dom0 and a
xenstore stubdom, dom0 can be handled as a regular XS_HVM following the
late init path.

Ideally we'd drop the use of xen_initial_domain() and just check for the
event channel instead.  However, ARM has a xen,enhanced no-xenstore
mode, where the event channel and PFN would both be 0.  Retain the
xen_initial_domain() check, and use that for an additional check when
the event channel is 0.

Check the full 64bit HVM_PARAM_STORE_EVTCHN value to catch the off
chance that high bits are set for the 32bit event channel.

Signed-off-by: Jason Andryuk <jason.andryuk@amd.com>
Change-Id: I5506da42e4c6b8e85079fefb2f193c8de17c7437
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Signed-off-by: Juergen Gross <jgross@suse.com>
Message-ID: <20250506204456.5220-1-jason.andryuk@amd.com>

Author: Jason Andryuk

drivers/xen/xenbus/xenbus_probe.c

@@ -966,9 +966,15 @@ static int __init xenbus_init(void)
 	if (xen_pv_domain())
 		xen_store_domain_type = XS_PV;
 	if (xen_hvm_domain())
+	{
 		xen_store_domain_type = XS_HVM;
-	if (xen_hvm_domain() && xen_initial_domain())
-		xen_store_domain_type = XS_LOCAL;
+		err = hvm_get_parameter(HVM_PARAM_STORE_EVTCHN, &v);
+		if (err)
+			goto out_error;
+		xen_store_evtchn = (int)v;
+		if (!v && xen_initial_domain())
+			xen_store_domain_type = XS_LOCAL;
+	}
 	if (xen_pv_domain() && !xen_start_info->store_evtchn)
 		xen_store_domain_type = XS_LOCAL;
 	if (xen_pv_domain() && xen_start_info->store_evtchn)
@@ -987,10 +993,6 @@ static int __init xenbus_init(void)
 		xen_store_interface = gfn_to_virt(xen_store_gfn);
 		break;
 	case XS_HVM:
-		err = hvm_get_parameter(HVM_PARAM_STORE_EVTCHN, &v);
-		if (err)
-			goto out_error;
-		xen_store_evtchn = (int)v;
 		err = hvm_get_parameter(HVM_PARAM_STORE_PFN, &v);
 		if (err)
 			goto out_error;