i386/apic: Skip kvm_apic_put() for TDX

KVM neithers allow writing to MSR_IA32_APICBASE for TDs, nor allow for
KVM_SET_LAPIC[*].

Note, KVM_GET_LAPIC is also disallowed for TDX. It is called in the path

  do_kvm_cpu_synchronize_state()
  -> kvm_arch_get_registers()
     -> kvm_get_apic()

and it's already disllowed for confidential guest through
guest_state_protected.

[*] https://lore.kernel.org/all/Z3w4Ku4Jq0CrtXne@google.com/

Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Link: https://lore.kernel.org/r/20250508150002.689633-42-xiaoyao.li@intel.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/hw/i386/kvm/apic.c b/hw/i386/kvm/apic.c
index 39035db0422ad1e6411eb8fd47fb49e4364fbf18..1be9bfe36e91157d5bd0c456cde9fbf6a885dc48 100644 (file)
--- a/hw/i386/kvm/apic.c
+++ b/hw/i386/kvm/apic.c
@@ -17,6 +17,7 @@
 #include "system/hw_accel.h"
 #include "system/kvm.h"
 #include "kvm/kvm_i386.h"
+#include "kvm/tdx.h"
 
 static inline void kvm_apic_set_reg(struct kvm_lapic_state *kapic,
                                     int reg_id, uint32_t val)
@@ -141,6 +142,10 @@ static void kvm_apic_put(CPUState *cs, run_on_cpu_data data)
     struct kvm_lapic_state kapic;
     int ret;
 
+    if (is_tdx_vm()) {
+        return;
+    }
+
     kvm_put_apicbase(s->cpu, s->apicbase);
     kvm_put_apic_state(s, &kapic);