[PATCH v2 05/17] xen/dom0less: Workaround XSM for evtchn_alloc_unbound

[Jason Andryuk <jason.andryuk@xxxxxxx>]

When used with an untargetable domain, xsm_evtchn_unbound fails even
though the idle domain has is_privileged = true.  Switch current to the
domain under construction so that event channel creation is allowed as
XSM_TARGET.

Signed-off-by: Jason Andryuk <jason.andryuk@xxxxxxx>
---
v2:
New

This was Jan's suggestion when dom0less originally had trouble with
evtchn_alloc_unbound() and xsm_set_system_active() was introduced.  As
noted, is_privileged is insufficient for operating on an untargetable
domain.
---
 xen/common/device-tree/dom0less-build.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/xen/common/device-tree/dom0less-build.c 
b/xen/common/device-tree/dom0less-build.c
index 22af043aa5..a2789e3bdf 100644
--- a/xen/common/device-tree/dom0less-build.c
+++ b/xen/common/device-tree/dom0less-build.c
@@ -77,11 +77,20 @@ bool __init is_dom0less_mode(void)
 static int __init alloc_xenstore_evtchn(struct domain *d)
 {
     evtchn_alloc_unbound_t alloc;
+    struct vcpu *old_current;
     int rc;
 
     alloc.dom = d->domain_id;
     alloc.remote_dom = xs_domid;
+    /*
+     * Switch current from the Xen idle vcpu to the domain's vcpu.  This is to
+     * pass the xsm_evtchn_unbound() check for an untargetable domain.
+     */
+    old_current = current;
+    set_current(d->vcpu[0]);
     rc = evtchn_alloc_unbound(&alloc, 0);
+    /* Restore Xen idle vcpu. */
+    set_current(old_current);
     if ( rc )
     {
         printk("Failed allocating event channel for domain\n");
-- 
2.50.0