Helper domctl_lock_{acquire,release} is domctl_lock, which HVM_PARAM_IDENT_PT
uses to ensure synchronization and hence being a toolstack-only operation.
So we shall make HVM_PARAM_IDENT_PT conditional upon CONFIG_MGMT_HYPERCALLS,
returning -EOPNOTSUPP when MGMT_HYPERCALLS=n.

Suggested-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Penny Zheng <Penny.Zheng@amd.com>
---
v2 -> v3:
- new commit
---
 xen/arch/x86/hvm/hvm.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index e77b0c03ed..e7d630af95 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -4281,7 +4281,6 @@ static int hvm_allow_set_param(struct domain *d,
 static int hvm_set_param(struct domain *d, uint32_t index, uint64_t value)
 {
     struct domain *curr_d = current->domain;
-    struct vcpu *v;
     int rc;
 
     rc = hvm_allow_set_param(d, index, value);
@@ -4307,6 +4306,10 @@ static int hvm_set_param(struct domain *d, uint32_t index, uint64_t value)
             rc = -EINVAL;
         break;
     case HVM_PARAM_IDENT_PT:
+    {
+#ifdef CONFIG_MGMT_HYPERCALLS
+        struct vcpu *v;
+
         /*
          * Only actually required for VT-x lacking unrestricted_guest
          * capabilities.  Short circuit the pause if possible.
@@ -4334,7 +4337,11 @@ static int hvm_set_param(struct domain *d, uint32_t index, uint64_t value)
         domain_unpause(d);
 
         domctl_lock_release();
+#else
+        rc = -EOPNOTSUPP;
+#endif /* CONFIG_MGMT_HYPERCALLS */
         break;
+    }
     case HVM_PARAM_DM_DOMAIN:
         /* The only value this should ever be set to is DOMID_SELF */
         if ( value != DOMID_SELF )
-- 
2.34.1

On 13.10.2025 12:15, Penny Zheng wrote:
> Helper domctl_lock_{acquire,release} is domctl_lock, which HVM_PARAM_IDENT_PT
> uses to ensure synchronization and hence being a toolstack-only operation.
> So we shall make HVM_PARAM_IDENT_PT conditional upon CONFIG_MGMT_HYPERCALLS,
> returning -EOPNOTSUPP when MGMT_HYPERCALLS=n.
> 
> Suggested-by: Jan Beulich <jbeulich@suse.com>

I fear this isn't quite what I suggested. The param get/set are XSM_TARGET, i.e.
can be used by DM as well. The particular one here shouldn't be used by a DM, but
that's a different question. Similarly in principle the PVH Dom0 building code
should be able to use this path; it doesn't right now in favor of some open-
coding.

What iirc I did suggest was that the serialization isn't needed when no domctl can
be used to otherwise alter (relevant) guest state.

Jan