kvm/xen-emu: re-initialize capabilities during confidential guest reset

On confidential guests KVM virtual machine file descriptor changes as a
part of the guest reset process. Xen capabilities needs to be re-initialized in
KVM against the new file descriptor.

Signed-off-by: Ani Sinha <anisinha@redhat.com>
Link: https://lore.kernel.org/r/20260225035000.385950-29-anisinha@redhat.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

target/i386/kvm/xen-emu.c

@@ -44,9 +44,12 @@
 
 #include "xen-compat.h"
 
+NotifierWithReturn xen_vmfd_change_notifier;
+static uint32_t xen_msr;
 static void xen_vcpu_singleshot_timer_event(void *opaque);
 static void xen_vcpu_periodic_timer_event(void *opaque);
 static int vcpuop_stop_singleshot_timer(CPUState *cs);
+static int do_initialize_xen_caps(KVMState *s, uint32_t hypercall_msr);
 
 #ifdef TARGET_X86_64
 #define hypercall_compat32(longmode) (!(longmode))
@@ -54,6 +57,23 @@ static int vcpuop_stop_singleshot_timer(CPUState *cs);
 #define hypercall_compat32(longmode) (false)
 #endif
 
+static int xen_handle_vmfd_change(NotifierWithReturn *n,
+                                  void *data, Error** errp)
+{
+    int ret;
+
+    /* we are not interested in pre vmfd change notification */
+    if (((VmfdChangeNotifier *)data)->pre) {
+        return 0;
+    }
+
+    ret = do_initialize_xen_caps(kvm_state, xen_msr);
+    if (ret < 0) {
+        return ret;
+    }
+    return 0;
+}
+
 static bool kvm_gva_to_gpa(CPUState *cs, uint64_t gva, uint64_t *gpa,
                            size_t *len, bool is_write)
 {
@@ -111,7 +131,7 @@ static inline int kvm_copy_to_gva(CPUState *cs, uint64_t gva, void *buf,
     return kvm_gva_rw(cs, gva, buf, sz, true);
 }
 
-int kvm_xen_init(KVMState *s, uint32_t hypercall_msr)
+static int do_initialize_xen_caps(KVMState *s, uint32_t hypercall_msr)
 {
     const int required_caps = KVM_XEN_HVM_CONFIG_HYPERCALL_MSR |
         KVM_XEN_HVM_CONFIG_INTERCEPT_HCALL | KVM_XEN_HVM_CONFIG_SHARED_INFO;
@@ -143,6 +163,19 @@ int kvm_xen_init(KVMState *s, uint32_t hypercall_msr)
                      strerror(-ret));
         return ret;
     }
+    return xen_caps;
+}
+
+int kvm_xen_init(KVMState *s, uint32_t hypercall_msr)
+{
+    int xen_caps;
+
+    xen_caps = do_initialize_xen_caps(s, hypercall_msr);
+    if (xen_caps < 0) {
+        return xen_caps;
+    }
+
+    xen_msr = hypercall_msr;
 
     /* If called a second time, don't repeat the rest of the setup. */
     if (s->xen_caps) {
@@ -185,6 +218,9 @@ int kvm_xen_init(KVMState *s, uint32_t hypercall_msr)
     xen_primary_console_reset();
     xen_xenstore_reset();
 
+    xen_vmfd_change_notifier.notify = xen_handle_vmfd_change;
+    kvm_vmfd_add_change_notifier(&xen_vmfd_change_notifier);
+
     return 0;
 }