ArmPkg/ArmMmuLib: don't replace table entries with block entries

Drop the optimization that replaces table entries with block entries and
frees the page tables in the subhierarchy that is being replaced. This
rarely occurs in practice anyway, and will require more elaborate TLB
maintenance once we switch to a different approach where we no longer
disable the MMU and nuke the TLB entirely every time we update a
descriptor in a way that requires break-before-make (BBM).

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

1 files changed, 2 insertions, 18 deletions

diff --git a/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c b/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c
index e5ecc73751..34f1031c4d 100644
--- a/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c
+++ b/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c
@@ -197,12 +197,9 @@ UpdateRegionMappingRecursive (
     // than a block, and recurse to create the block or page entries at

     // the next level. No block mappings are allowed at all at level 0,

     // so in that case, we have to recurse unconditionally.

-    // If we are changing a table entry and the AttributeClearMask is non-zero,

-    // we cannot replace it with a block entry without potentially losing

-    // attribute information, so keep the table entry in that case.

     //

     if ((Level == 0) || (((RegionStart | BlockEnd) & BlockMask) != 0) ||

-        (IsTableEntry (*Entry, Level) && (AttributeClearMask != 0)))

+        IsTableEntry (*Entry, Level))

     {

       ASSERT (Level < 3);

 

@@ -294,20 +291,7 @@ UpdateRegionMappingRecursive (
       EntryValue |= (Level == 3) ? TT_TYPE_BLOCK_ENTRY_LEVEL3

                                  : TT_TYPE_BLOCK_ENTRY;

 

-      if (IsTableEntry (*Entry, Level)) {

-        //

-        // We are replacing a table entry with a block entry. This is only

-        // possible if we are keeping none of the original attributes.

-        // We can free the table entry's page table, and all the ones below

-        // it, since we are dropping the only possible reference to it.

-        //

-        ASSERT (AttributeClearMask == 0);

-        TranslationTable = (VOID *)(UINTN)(*Entry & TT_ADDRESS_MASK_BLOCK_ENTRY);

-        ReplaceTableEntry (Entry, EntryValue, RegionStart, TRUE);

-        FreePageTablesRecursive (TranslationTable, Level + 1);

-      } else {

-        ReplaceTableEntry (Entry, EntryValue, RegionStart, FALSE);

-      }

+      ReplaceTableEntry (Entry, EntryValue, RegionStart, FALSE);

     }

   }