ArmPkg/ArmMmuLib: Reuse XIP MMU routines when splitting entries

In order to reduce the likelihood that we will need to rely on the logic
that disables and re-enables the MMU for updating a page table entry
safely, expose the XIP version of the helper routine via a HOB and use
it instead of the one that is copied into DRAM. Since the XIP copy is
already clean to the PoC, and will never end up getting unmapped during
a block entry split, we can use it safely without any cache maintenance,
and without running the risk of pulling the rug from under our feet when
updating an entry by going through an invalid mapping.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Leif Lindholm <quic_llindhol@quicinc.com>

ArmPkg/ArmPkg.dec

@@ -99,6 +99,8 @@
   # Include/Guid/ArmMpCoreInfo.h
   gArmMpCoreInfoGuid = { 0xa4ee0728, 0xe5d7, 0x4ac5,  {0xb2, 0x1e, 0x65, 0x8e, 0xd8, 0x57, 0xe8, 0x34} }
 
+  gArmMmuReplaceLiveTranslationEntryFuncGuid = { 0xa8b50ff3, 0x08ec, 0x4dd3, {0xbf, 0x04, 0x28, 0xbf, 0x71, 0x75, 0xc7, 0x4a} }
+
 [Protocols.common]
   ## Arm System Control and Management Interface(SCMI) Base protocol
   ## ArmPkg/Include/Protocol/ArmScmiBaseProtocol.h

ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c

@@ -10,6 +10,7 @@
 **/
 
 #include <Uefi.h>
+#include <Pi/PiMultiPhase.h>
 #include <Chipset/AArch64.h>
 #include <Library/BaseMemoryLib.h>
 #include <Library/CacheMaintenanceLib.h>
@@ -120,14 +121,14 @@ ReplaceTableEntry (
     // use an ordinary break before make. Otherwise, we will need to
     // temporarily disable the MMU.
     DisableMmu = FALSE;
-    if ((((RegionStart ^ (UINTN)ArmReplaceLiveTranslationEntry) & ~BlockMask) == 0) ||
+    if ((((RegionStart ^ (UINTN)mReplaceLiveEntryFunc) & ~BlockMask) == 0) ||
         (((RegionStart ^ (UINTN)Entry) & ~BlockMask) == 0))
     {
       DisableMmu = TRUE;
       DEBUG ((DEBUG_WARN, "%a: splitting block entry with MMU disabled\n", __FUNCTION__));
     }
 
-    ArmReplaceLiveTranslationEntry (Entry, Value, RegionStart, DisableMmu);
+    mReplaceLiveEntryFunc (Entry, Value, RegionStart, DisableMmu);
   }
 }
 
@@ -747,15 +748,21 @@ ArmMmuBaseLibConstructor (
   )
 {
   extern UINT32  ArmReplaceLiveTranslationEntrySize;
+  VOID           *Hob;
 
-  //
-  // The ArmReplaceLiveTranslationEntry () helper function may be invoked
-  // with the MMU off so we have to ensure that it gets cleaned to the PoC
-  //
-  WriteBackDataCacheRange (
-    (VOID *)(UINTN)ArmReplaceLiveTranslationEntry,
-    ArmReplaceLiveTranslationEntrySize
-    );
+  Hob = GetFirstGuidHob (&gArmMmuReplaceLiveTranslationEntryFuncGuid);
+  if (Hob != NULL) {
+    mReplaceLiveEntryFunc = *(VOID **)GET_GUID_HOB_DATA (Hob);
+  } else {
+    //
+    // The ArmReplaceLiveTranslationEntry () helper function may be invoked
+    // with the MMU off so we have to ensure that it gets cleaned to the PoC
+    //
+    WriteBackDataCacheRange (
+      (VOID *)(UINTN)ArmReplaceLiveTranslationEntry,
+      ArmReplaceLiveTranslationEntrySize
+      );
+  }
 
   return RETURN_SUCCESS;
 }

ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuPeiLibConstructor.c

@@ -12,6 +12,7 @@
 #include <Library/ArmMmuLib.h>
 #include <Library/CacheMaintenanceLib.h>
 #include <Library/DebugLib.h>
+#include <Library/HobLib.h>
 
 EFI_STATUS
 EFIAPI
@@ -21,6 +22,8 @@ ArmMmuPeiLibConstructor (
   )
 {
   extern UINT32  ArmReplaceLiveTranslationEntrySize;
+  VOID           *ArmReplaceLiveTranslationEntryFunc;
+  VOID           *Hob;
 
   EFI_FV_FILE_INFO  FileInfo;
   EFI_STATUS        Status;
@@ -42,6 +45,20 @@ ArmMmuPeiLibConstructor (
        (UINTN)ArmReplaceLiveTranslationEntry + ArmReplaceLiveTranslationEntrySize))
   {
     DEBUG ((DEBUG_INFO, "ArmMmuLib: skipping cache maintenance on XIP PEIM\n"));
+
+    //
+    // Expose the XIP version of the ArmReplaceLiveTranslationEntry() routine
+    // via a HOB so we can fall back to it later when we need to split block
+    // mappings in a way that adheres to break-before-make requirements.
+    //
+    ArmReplaceLiveTranslationEntryFunc = ArmReplaceLiveTranslationEntry;
+
+    Hob = BuildGuidDataHob (
+            &gArmMmuReplaceLiveTranslationEntryFuncGuid,
+            &ArmReplaceLiveTranslationEntryFunc,
+            sizeof ArmReplaceLiveTranslationEntryFunc
+            );
+    ASSERT (Hob != NULL);
   } else {
     DEBUG ((DEBUG_INFO, "ArmMmuLib: performing cache maintenance on shadowed PEIM\n"));
     //

ArmPkg/Library/ArmMmuLib/ArmMmuBaseLib.inf

@@ -36,7 +36,11 @@
 [LibraryClasses]
   ArmLib
   CacheMaintenanceLib
+  HobLib
   MemoryAllocationLib
 
+[Guids]
+  gArmMmuReplaceLiveTranslationEntryFuncGuid
+
 [Pcd.ARM]
   gArmTokenSpaceGuid.PcdNormalMemoryNonshareableOverride

ArmPkg/Library/ArmMmuLib/ArmMmuPeiLib.inf

@@ -29,4 +29,8 @@
 [LibraryClasses]
   ArmLib
   CacheMaintenanceLib
+  HobLib
   MemoryAllocationLib
+
+[Guids]
+  gArmMmuReplaceLiveTranslationEntryFuncGuid