OvmfPkg/IoMmuDxe: propagate errors from AmdSevInstallIoMmuProtocol()

If we cannot install the IOMMU protocol for whatever reason, exit the
driver with an error. The same is already done for the IOMMU Absent
protocol.

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Brijesh Singh <brijesh.singh@amd.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Tested-by: Brijesh Singh <brijesh.singh@amd.com>
Reviewed-by: Brijesh Singh <brijesh.singh@amd.com>

OvmfPkg/IoMmuDxe/AmdSevIoMmu.c

@@ -499,7 +499,7 @@ EDKII_IOMMU_PROTOCOL  mAmdSev = {
   Initialize Iommu Protocol.
 
 **/
-VOID
+EFI_STATUS
 EFIAPI
 AmdSevInstallIoMmuProtocol (
   VOID
@@ -514,5 +514,5 @@ AmdSevInstallIoMmuProtocol (
                   &gEdkiiIoMmuProtocolGuid, &mAmdSev,
                   NULL
                   );
-  ASSERT_EFI_ERROR (Status);
+  return Status;
 }

OvmfPkg/IoMmuDxe/AmdSevIoMmu.h

@@ -35,7 +35,7 @@
   MemEncryptSevLib.
 
 **/
-VOID
+EFI_STATUS
 EFIAPI
 AmdSevInstallIoMmuProtocol (
   VOID

OvmfPkg/IoMmuDxe/IoMmuDxe.c

@@ -36,14 +36,12 @@ IoMmuDxeEntryPoint (
   EFI_STATUS    Status;
   EFI_HANDLE    Handle;
 
-  Status = EFI_SUCCESS;
-
   //
   // When SEV is enabled, install IoMmu protocol otherwise install the
   // placeholder protocol so that other dependent module can run.
   //
   if (MemEncryptSevIsEnabled ()) {
-    AmdSevInstallIoMmuProtocol ();
+    Status = AmdSevInstallIoMmuProtocol ();
   } else {
     Handle = NULL;