[RFC PATCH 07/14] OvmfPkg/AmdSev: MH support for mailbox protocol

["Tobin Feldman-Fitzthum" <tobin@linux.ibm.com>]

The migration handler communicates with the hypervisor
via a shared mailbox page. The MH can perform four functions
at the behest of the HV: init, save page, restore page, and
reset.

Signed-off-by: Tobin Feldman-Fitzthum <tobin@linux.ibm.com>
---
 .../ConfidentialMigrationDxe.inf              |  1 +
 .../ConfidentialMigrationDxe.c                | 78 +++++++++++++++++++
 2 files changed, 79 insertions(+)

diff --git a/OvmfPkg/AmdSev/ConfidentialMigration/ConfidentialMigrationDxe.inf b/OvmfPkg/AmdSev/ConfidentialMigration/ConfidentialMigrationDxe.inf
index a4906a2451..49457d5d17 100644
--- a/OvmfPkg/AmdSev/ConfidentialMigration/ConfidentialMigrationDxe.inf
+++ b/OvmfPkg/AmdSev/ConfidentialMigration/ConfidentialMigrationDxe.inf
@@ -34,6 +34,7 @@
 [Pcd]
   gUefiOvmfPkgTokenSpaceGuid.PcdIsConfidentialMigrationTarget
   gUefiOvmfPkgTokenSpaceGuid.PcdStartConfidentialMigrationHandler
+  gUefiOvmfPkgTokenSpaceGuid.PcdConfidentialMigrationMailboxBase
 
 [Depex]
   gEfiMpServiceProtocolGuid
diff --git a/OvmfPkg/AmdSev/ConfidentialMigration/ConfidentialMigrationDxe.c b/OvmfPkg/AmdSev/ConfidentialMigration/ConfidentialMigrationDxe.c
index 6d9fe7043b..8402fcc4fa 100644
--- a/OvmfPkg/AmdSev/ConfidentialMigration/ConfidentialMigrationDxe.c
+++ b/OvmfPkg/AmdSev/ConfidentialMigration/ConfidentialMigrationDxe.c
@@ -9,16 +9,94 @@
 #include <Library/UefiRuntimeServicesTableLib.h>
 #include <Library/DebugLib.h>
 #include <Protocol/MpService.h>
+#include <Library/BaseMemoryLib.h>
 
+//
+// Functions implemented by the migration handler
+//
+#define MH_FUNC_INIT          0
+#define MH_FUNC_SAVE_PAGE     1
+#define MH_FUNC_RESTORE_PAGE  2
+#define MH_FUNC_RESET         3
+
+//
+// Return codes for MH functions
+//
+#define MH_SUCCESS            0
+#define MH_INVALID_FUNC     (-1)
+#define MH_AUTH_ERR         (-2)
+
+//
+// Index of CPU that MH runs on.
+//
 UINTN MigrationHandlerCpuIndex;
 
+//
+// Mailbox for communication with hypervisor
+//
+typedef volatile struct {
+  UINT64       nr;
+  UINT64       gpa;
+  UINT32       do_prefetch;
+  UINT32       ret;
+  UINT32       go;
+  UINT32       done;
+} MH_COMMAND_PARAMETERS;
+
+
 VOID
 EFIAPI
 MigrationHandlerMain (
   IN OUT VOID *Buffer
   )
 {
+  UINT64                       params_base;
+  MH_COMMAND_PARAMETERS        *params;
+  VOID                         *page_va;
+
   DebugPrint (DEBUG_INFO,"MIGRATION Handler Started\n");
+
+  params_base = PcdGet32 (PcdConfidentialMigrationMailboxBase);
+  params = (VOID *)params_base;
+  page_va = (VOID *)params_base + 0x1000;
+
+  DisableInterrupts();
+  params->go = 0;
+
+  while (1) {
+    while (!params->go) {
+      CpuPause();
+    }
+    params->done = 0;
+
+    switch (params->nr) {
+    case MH_FUNC_INIT:
+      params->ret = MH_SUCCESS;
+      break;
+
+    case MH_FUNC_SAVE_PAGE:
+      CopyMem(page_va, (VOID *)params->gpa, 4096);
+      params->ret = MH_SUCCESS;
+      break;
+
+    case MH_FUNC_RESTORE_PAGE:
+      CopyMem((VOID *)params->gpa, page_va, 4096);
+      params->ret = MH_SUCCESS;
+      break;
+
+    case MH_FUNC_RESET:
+      params->ret = MH_SUCCESS;
+      break;
+
+    default:
+      params->ret = MH_INVALID_FUNC;
+      break;
+    }
+
+    params->go = 0;
+    params->done = 1;
+
+  }
 }
 
 EFI_STATUS
-- 
2.20.1