Allow to use Xen hypercalls earlier, during the PEIM stage, but
XenHypercallLibInit() must be called once the XenInfo HOB is created
with the HyperPage setup.

Change the return value of XenHypercallLibInit so failure can be
detected when the call shouldn't fail, but still have the constructor
always succeed.

Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=1689
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
---

Notes:
    v3:
    - only modify XenHypercallLib, and to the modification of XenPlatformPei
      in a separated patch.
    - Allow XenHypercallLibInit to be called outside the library instead of
      creating a new function, but also return failure on failure,
      and have a new constructor that never fail.

 .../Library/XenHypercallLib/XenHypercallLib.inf  |  4 ++--
 OvmfPkg/Include/Library/XenHypercallLib.h        | 12 ++++++++++++
 .../Library/XenHypercallLib/X86XenHypercall.c    |  8 +-------
 OvmfPkg/Library/XenHypercallLib/XenHypercall.c   | 16 ++++++++++++++++
 4 files changed, 31 insertions(+), 9 deletions(-)

diff --git a/OvmfPkg/Library/XenHypercallLib/XenHypercallLib.inf b/OvmfPkg/Library/XenHypercallLib/XenHypercallLib.inf
index 1208f0057a..21ce5b4434 100644
--- a/OvmfPkg/Library/XenHypercallLib/XenHypercallLib.inf
+++ b/OvmfPkg/Library/XenHypercallLib/XenHypercallLib.inf
@@ -12,10 +12,10 @@ [Defines]
   FILE_GUID                      = B5EE9A32-CA5A-49A8-82E3-ADA4CCB77C7C
   MODULE_TYPE                    = BASE
   VERSION_STRING                 = 1.0
-  CONSTRUCTOR                    = XenHypercallLibInit
+  CONSTRUCTOR                    = XenHypercallLibConstruct
 
 [Defines.IA32, Defines.X64]
-  LIBRARY_CLASS                  = XenHypercallLib|DXE_DRIVER UEFI_DRIVER
+  LIBRARY_CLASS                  = XenHypercallLib|PEIM DXE_DRIVER UEFI_DRIVER
 
 [Defines.ARM, Defines.AARCH64]
   LIBRARY_CLASS                  = XenHypercallLib
diff --git a/OvmfPkg/Include/Library/XenHypercallLib.h b/OvmfPkg/Include/Library/XenHypercallLib.h
index c43822782b..c1491dd652 100644
--- a/OvmfPkg/Include/Library/XenHypercallLib.h
+++ b/OvmfPkg/Include/Library/XenHypercallLib.h
@@ -10,6 +10,18 @@
 #ifndef __XEN_HYPERCALL_LIB_H__
 #define __XEN_HYPERCALL_LIB_H__
 
+/**
+  To call when the gEfiXenInfoGuid HOB became available after the library init
+  function has already been executed.
+
+  This allow to make hypercall in the PEIM stage.
+**/
+RETURN_STATUS
+EFIAPI
+XenHypercallLibInit (
+  VOID
+  );
+
 /**
   Check if the Xen Hypercall library is able to make calls to the Xen
   hypervisor.
diff --git a/OvmfPkg/Library/XenHypercallLib/X86XenHypercall.c b/OvmfPkg/Library/XenHypercallLib/X86XenHypercall.c
index 27083f924f..f779e46470 100644
--- a/OvmfPkg/Library/XenHypercallLib/X86XenHypercall.c
+++ b/OvmfPkg/Library/XenHypercallLib/X86XenHypercall.c
@@ -59,13 +59,7 @@ XenHypercallLibInit (
 
   GuidHob = GetFirstGuidHob (&gEfiXenInfoGuid);
   if (GuidHob == NULL) {
-    //
-    // We don't fail library construction, since that has catastrophic
-    // consequences for client modules (whereas those modules may easily be
-    // running on a non-Xen platform). Instead, XenHypercallIsAvailable() above
-    // will return FALSE.
-    //
-    return RETURN_SUCCESS;
+    return RETURN_NOT_FOUND;
   }
   XenInfo = (EFI_XEN_INFO *) GET_GUID_HOB_DATA (GuidHob);
   HyperPage = XenInfo->HyperPages;
diff --git a/OvmfPkg/Library/XenHypercallLib/XenHypercall.c b/OvmfPkg/Library/XenHypercallLib/XenHypercall.c
index a2c41a2a69..d4fa802743 100644
--- a/OvmfPkg/Library/XenHypercallLib/XenHypercall.c
+++ b/OvmfPkg/Library/XenHypercallLib/XenHypercall.c
@@ -15,6 +15,22 @@
 #include <Library/DebugLib.h>
 #include <Library/XenHypercallLib.h>
 
+RETURN_STATUS
+EFIAPI
+XenHypercallLibConstruct (
+  VOID
+  )
+{
+  XenHypercallLibInit ();
+  //
+  // We don't fail library construction, since that has catastrophic
+  // consequences for client modules (whereas those modules may easily be
+  // running on a non-Xen platform). Instead, XenHypercallIsAvailable()
+  // will return FALSE.
+  //
+  return RETURN_SUCCESS;
+}
+
 UINT64
 EFIAPI
 XenHypercallHvmGetParam (
-- 
Anthony PERARD

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