Re: [PATCH v3 1/2] ArmPkg/ArmMmuLib AARCH64: rewrite page table code

["Leif Lindholm" <leif@nuviainc.com>]

On Fri, Mar 06, 2020 at 17:12:45 +0100, Ard Biesheuvel wrote:
> Replace the slightly overcomplicated page table management code with
> a simplified, recursive implementation that should be far easier to
> reason about.
> 
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> ---
>  ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c | 332 +++++++-------------
>  1 file changed, 108 insertions(+), 224 deletions(-)
> 
> diff --git a/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c b/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c
> index 204e33c75f95..e36594fea3ad 100644
> --- a/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c
> +++ b/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c
> @@ -121,14 +121,16 @@ GetRootTranslationTableInfo (
>  
>  STATIC
>  VOID
> -ReplaceLiveEntry (
> +ReplaceTableEntry (
>    IN  UINT64  *Entry,
>    IN  UINT64  Value,
> -  IN  UINT64  RegionStart
> +  IN  UINT64  RegionStart,
> +  IN  BOOLEAN IsLiveBlockMapping
>    )
>  {
> -  if (!ArmMmuEnabled ()) {
> +  if (!ArmMmuEnabled () || !IsLiveBlockMapping) {
>      *Entry = Value;
> +    ArmUpdateTranslationTableEntry (Entry, (VOID *)(UINTN)RegionStart);
>    } else {
>      ArmReplaceLiveTranslationEntry (Entry, Value, RegionStart);
>    }
> @@ -165,229 +167,132 @@ LookupAddresstoRootTable (
>  }
>  
>  STATIC
> -UINT64*
> -GetBlockEntryListFromAddress (
> -  IN  UINT64       *RootTable,
> -  IN  UINT64        RegionStart,
> -  OUT UINTN        *TableLevel,
> -  IN OUT UINT64    *BlockEntrySize,
> -  OUT UINT64      **LastBlockEntry
> +EFI_STATUS
> +UpdateRegionMappingRec (

What does Rec stand for? Record? Recursively?
Could it be written out?

> +  IN  UINT64      RegionStart,
> +  IN  UINT64      RegionEnd,
> +  IN  UINT64      AttributeSetMask,
> +  IN  UINT64      AttributeClearMask,
> +  IN  UINT64      *PageTable,
> +  IN  UINTN       Level

This sets the scene for a spectacularly unhelpful diff.
Would you consider adding UpdateRegionMappingRec() *before*
LookupAddresstoRootTable() for the only purpose of working against the
shortcomings of the line diff algorithm? That is what I ended up doing
locally for the review.

>    )
>  {
> -  UINTN   RootTableLevel;
> -  UINTN   RootTableEntryCount;
> -  UINT64 *TranslationTable;
> -  UINT64 *BlockEntry;
> -  UINT64 *SubTableBlockEntry;
> -  UINT64  BlockEntryAddress;
> -  UINTN   BaseAddressAlignment;
> -  UINTN   PageLevel;
> -  UINTN   Index;
> -  UINTN   IndexLevel;
> -  UINTN   T0SZ;
> -  UINT64  Attributes;
> -  UINT64  TableAttributes;
> -
> -  // Initialize variable
> -  BlockEntry = NULL;
> -
> -  // Ensure the parameters are valid
> -  if (!(TableLevel && BlockEntrySize && LastBlockEntry)) {
> -    ASSERT_EFI_ERROR (EFI_INVALID_PARAMETER);
> -    return NULL;
> -  }
> -
> -  // Ensure the Region is aligned on 4KB boundary
> -  if ((RegionStart & (SIZE_4KB - 1)) != 0) {
> -    ASSERT_EFI_ERROR (EFI_INVALID_PARAMETER);
> -    return NULL;
> -  }
> -
> -  // Ensure the required size is aligned on 4KB boundary and not 0
> -  if ((*BlockEntrySize & (SIZE_4KB - 1)) != 0 || *BlockEntrySize == 0) {
> -    ASSERT_EFI_ERROR (EFI_INVALID_PARAMETER);
> -    return NULL;
> -  }
> -
> -  T0SZ = ArmGetTCR () & TCR_T0SZ_MASK;
> -  // Get the Table info from T0SZ
> -  GetRootTranslationTableInfo (T0SZ, &RootTableLevel, &RootTableEntryCount);
> -
> -  // If the start address is 0x0 then we use the size of the region to identify the alignment
> -  if (RegionStart == 0) {
> -    // Identify the highest possible alignment for the Region Size
> -    BaseAddressAlignment = LowBitSet64 (*BlockEntrySize);
> -  } else {
> -    // Identify the highest possible alignment for the Base Address
> -    BaseAddressAlignment = LowBitSet64 (RegionStart);
> -  }
> -
> -  // Identify the Page Level the RegionStart must belong to. Note that PageLevel
> -  // should be at least 1 since block translations are not supported at level 0
> -  PageLevel = MAX (3 - ((BaseAddressAlignment - 12) / 9), 1);
> -
> -  // If the required size is smaller than the current block size then we need to go to the page below.
> -  // The PageLevel was calculated on the Base Address alignment but did not take in account the alignment
> -  // of the allocation size
> -  while (*BlockEntrySize < TT_BLOCK_ENTRY_SIZE_AT_LEVEL (PageLevel)) {
> -    // It does not fit so we need to go a page level above
> -    PageLevel++;
> -  }
> -
> -  //
> -  // Get the Table Descriptor for the corresponding PageLevel. We need to decompose RegionStart to get appropriate entries
> -  //
> -
> -  TranslationTable = RootTable;
> -  for (IndexLevel = RootTableLevel; IndexLevel <= PageLevel; IndexLevel++) {
> -    BlockEntry = (UINT64*)TT_GET_ENTRY_FOR_ADDRESS (TranslationTable, IndexLevel, RegionStart);
> -
> -    if ((IndexLevel != 3) && ((*BlockEntry & TT_TYPE_MASK) == TT_TYPE_TABLE_ENTRY)) {
> -      // Go to the next table
> -      TranslationTable = (UINT64*)(*BlockEntry & TT_ADDRESS_MASK_DESCRIPTION_TABLE);
> -
> -      // If we are at the last level then update the last level to next level
> -      if (IndexLevel == PageLevel) {
> -        // Enter the next level
> -        PageLevel++;
> -      }
> -    } else if ((*BlockEntry & TT_TYPE_MASK) == TT_TYPE_BLOCK_ENTRY) {
> -      // If we are not at the last level then we need to split this BlockEntry
> -      if (IndexLevel != PageLevel) {
> -        // Retrieve the attributes from the block entry
> -        Attributes = *BlockEntry & TT_ATTRIBUTES_MASK;
> -
> -        // Convert the block entry attributes into Table descriptor attributes
> -        TableAttributes = TT_TABLE_AP_NO_PERMISSION;
> -        if (Attributes & TT_NS) {
> -          TableAttributes = TT_TABLE_NS;
> +  UINTN           BlockShift;
> +  UINT64          BlockMask;
> +  UINT64          BlockEnd;
> +  UINT64          *Entry;
> +  UINT64          EntryValue;
> +  VOID            *TranslationTable;
> +  EFI_STATUS      Status;
> +
> +  ASSERT (((RegionStart | RegionEnd) & EFI_PAGE_MASK) == 0);
> +
> +  BlockShift = (Level + 1) * BITS_PER_LEVEL + MIN_T0SZ;
> +  BlockMask = MAX_UINT64 >> BlockShift;
> +
> +  DEBUG ((DEBUG_VERBOSE, "%a(%d): %llx - %llx set %lx clr %lx\n", __FUNCTION__,
> +    Level, RegionStart, RegionEnd, AttributeSetMask, AttributeClearMask));
> +
> +  for (; RegionStart < RegionEnd; RegionStart = BlockEnd) {
> +    BlockEnd = MIN (RegionEnd, (RegionStart | BlockMask) + 1);
> +    Entry = &PageTable[(RegionStart >> (64 - BlockShift)) & (TT_ENTRY_COUNT - 1)];
> +
> +    //
> +    // If RegionStart or BlockEnd is not aligned to the block size at this
> +    // level, we will have to create a table mapping in order to map less
> +    // 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 (Level == 0 || ((RegionStart | BlockEnd) & BlockMask) != 0) {
> +      ASSERT (Level < 3);
> +
> +      if ((*Entry & TT_TYPE_MASK) != TT_TYPE_TABLE_ENTRY) {
> +        //
> +        // No table entry exists yet, so we need to allocate a page table
> +        // for the next level.
> +        //
> +        TranslationTable = AllocatePages (1);
> +        if (TranslationTable == NULL) {
> +          return EFI_OUT_OF_RESOURCES;
>          }
>  
> -        // Get the address corresponding at this entry
> -        BlockEntryAddress = RegionStart;
> -        BlockEntryAddress = BlockEntryAddress >> TT_ADDRESS_OFFSET_AT_LEVEL(IndexLevel);
> -        // Shift back to right to set zero before the effective address
> -        BlockEntryAddress = BlockEntryAddress << TT_ADDRESS_OFFSET_AT_LEVEL(IndexLevel);
> -
> -        // Set the correct entry type for the next page level
> -        if ((IndexLevel + 1) == 3) {
> -          Attributes |= TT_TYPE_BLOCK_ENTRY_LEVEL3;
> +        if ((*Entry & TT_TYPE_MASK) == TT_TYPE_BLOCK_ENTRY) {
> +          //
> +          // We are splitting an existing block entry, so we have to populate
> +          // the new table with the attributes of the block entry it replaces.
> +          //
> +          Status = UpdateRegionMappingRec (
> +                     RegionStart & ~BlockMask,
> +                     (RegionStart | BlockMask) + 1,
> +                     *Entry & TT_ATTRIBUTES_MASK,
> +                     0,
> +                     TranslationTable,
> +                     Level + 1);
> +          if (EFI_ERROR (Status)) {

I realise a EFI_OUT_OF_RESOURCES return value here means we would be
in dire straits already, but it would be nice if we could free the
local TranslationTable instead of leaking all allocations through the
tree.

If not worth the effort (or impossible condition), would still be
worth an explicit comment here.

> +            return Status;
> +          }
>          } else {
> -          Attributes |= TT_TYPE_BLOCK_ENTRY;
> +          ZeroMem (TranslationTable, EFI_PAGE_SIZE);
>          }
> +      } else {
> +        TranslationTable = (VOID *)(UINTN)(*Entry & TT_ADDRESS_MASK_BLOCK_ENTRY);
> +      }
>  
> -        // Create a new translation table
> -        TranslationTable = AllocatePages (1);
> -        if (TranslationTable == NULL) {
> -          return NULL;
> -        }
> -
> -        // Populate the newly created lower level table
> -        SubTableBlockEntry = TranslationTable;
> -        for (Index = 0; Index < TT_ENTRY_COUNT; Index++) {
> -          *SubTableBlockEntry = Attributes | (BlockEntryAddress + (Index << TT_ADDRESS_OFFSET_AT_LEVEL(IndexLevel + 1)));
> -          SubTableBlockEntry++;
> -        }
> +      //
> +      // Recurse to the next level
> +      //
> +      Status = UpdateRegionMappingRec (
> +                 RegionStart,
> +                 BlockEnd,
> +                 AttributeSetMask,
> +                 AttributeClearMask,
> +                 TranslationTable,
> +                 Level + 1);
> +      if (EFI_ERROR (Status)) {
> +        return Status;
> +      }
>  
> -        // Fill the BlockEntry with the new TranslationTable
> -        ReplaceLiveEntry (BlockEntry,
> -          (UINTN)TranslationTable | TableAttributes | TT_TYPE_TABLE_ENTRY,
> -          RegionStart);
> +      if ((*Entry & TT_TYPE_MASK) != TT_TYPE_TABLE_ENTRY) {
> +        ReplaceTableEntry (Entry,
> +          (UINT64)TranslationTable | TT_TYPE_TABLE_ENTRY,
> +          RegionStart,
> +          (*Entry & TT_TYPE_MASK) == TT_TYPE_BLOCK_ENTRY);
>        }
>      } else {
> -      if (IndexLevel != PageLevel) {
> -        //
> -        // Case when we have an Invalid Entry and we are at a page level above of the one targetted.
> -        //
> +      EntryValue = (*Entry & AttributeClearMask) | AttributeSetMask;
> +      EntryValue |= RegionStart;
> +      EntryValue |= (Level == 3) ? TT_TYPE_BLOCK_ENTRY_LEVEL3
> +                                 : TT_TYPE_BLOCK_ENTRY;
>  
> -        // Create a new translation table
> -        TranslationTable = AllocatePages (1);
> -        if (TranslationTable == NULL) {
> -          return NULL;
> -        }
> -
> -        ZeroMem (TranslationTable, TT_ENTRY_COUNT * sizeof(UINT64));
> -
> -        // Fill the new BlockEntry with the TranslationTable
> -        *BlockEntry = ((UINTN)TranslationTable & TT_ADDRESS_MASK_DESCRIPTION_TABLE) | TT_TYPE_TABLE_ENTRY;
> -      }
> +      ReplaceTableEntry (Entry, EntryValue, RegionStart, FALSE);
>      }
>    }
> -
> -  // Expose the found PageLevel to the caller
> -  *TableLevel = PageLevel;
> -
> -  // Now, we have the Table Level we can get the Block Size associated to this table
> -  *BlockEntrySize = TT_BLOCK_ENTRY_SIZE_AT_LEVEL (PageLevel);
> -
> -  // The last block of the root table depends on the number of entry in this table,
> -  // otherwise it is always the (TT_ENTRY_COUNT - 1)th entry in the table.
> -  *LastBlockEntry = TT_LAST_BLOCK_ADDRESS(TranslationTable,
> -      (PageLevel == RootTableLevel) ? RootTableEntryCount : TT_ENTRY_COUNT);
> -
> -  return BlockEntry;
> +  return EFI_SUCCESS;
>  }
>  
>  STATIC
>  EFI_STATUS
>  UpdateRegionMapping (
> -  IN  UINT64  *RootTable,
> -  IN  UINT64  RegionStart,
> -  IN  UINT64  RegionLength,
> -  IN  UINT64  Attributes,
> -  IN  UINT64  BlockEntryMask
> +  IN  UINT64                        RegionStart,
> +  IN  UINT64                        RegionSize,
> +  IN  UINT64                        AttributeSetMask,
> +  IN  UINT64                        AttributeClearMask

The new indentation here (which arguably is an improvement) sort of
masks the unchanged input RegionStart and the rename of
RegionLength->RegionSize. Since it doesn't help anything in this
series, could it be deferred (or broken out)?

>    )
>  {
> -  UINT32  Type;
> -  UINT64  *BlockEntry;
> -  UINT64  *LastBlockEntry;
> -  UINT64  BlockEntrySize;
> -  UINTN   TableLevel;
> +  UINTN     RootTableLevel;
> +  UINTN     T0SZ;
>  
> -  // Ensure the Length is aligned on 4KB boundary
> -  if ((RegionLength == 0) || ((RegionLength & (SIZE_4KB - 1)) != 0)) {
> -    ASSERT_EFI_ERROR (EFI_INVALID_PARAMETER);
> +  if ((RegionStart & EFI_PAGE_MASK) != 0 || (RegionSize & EFI_PAGE_MASK) != 0) {
>      return EFI_INVALID_PARAMETER;
>    }
>  
> -  do {
> -    // Get the first Block Entry that matches the Virtual Address and also the information on the Table Descriptor
> -    // such as the size of the Block Entry and the address of the last BlockEntry of the Table Descriptor
> -    BlockEntrySize = RegionLength;
> -    BlockEntry = GetBlockEntryListFromAddress (RootTable, RegionStart, &TableLevel, &BlockEntrySize, &LastBlockEntry);
> -    if (BlockEntry == NULL) {
> -      // GetBlockEntryListFromAddress() return NULL when it fails to allocate new pages from the Translation Tables
> -      return EFI_OUT_OF_RESOURCES;
> -    }
> +  T0SZ = ArmGetTCR () & TCR_T0SZ_MASK;
> +  GetRootTranslationTableInfo (T0SZ, &RootTableLevel, NULL);
>  
> -    if (TableLevel != 3) {
> -      Type = TT_TYPE_BLOCK_ENTRY;
> -    } else {
> -      Type = TT_TYPE_BLOCK_ENTRY_LEVEL3;
> -    }
> -
> -    do {
> -      // Fill the Block Entry with attribute and output block address
> -      *BlockEntry &= BlockEntryMask;
> -      *BlockEntry |= (RegionStart & TT_ADDRESS_MASK_BLOCK_ENTRY) | Attributes | Type;
> -
> -      ArmUpdateTranslationTableEntry (BlockEntry, (VOID *)RegionStart);
> -
> -      // Go to the next BlockEntry
> -      RegionStart += BlockEntrySize;
> -      RegionLength -= BlockEntrySize;
> -      BlockEntry++;
> -
> -      // Break the inner loop when next block is a table
> -      // Rerun GetBlockEntryListFromAddress to avoid page table memory leak
> -      if (TableLevel != 3 && BlockEntry <= LastBlockEntry &&
> -          (*BlockEntry & TT_TYPE_MASK) == TT_TYPE_TABLE_ENTRY) {
> -            break;
> -      }
> -    } while ((RegionLength >= BlockEntrySize) && (BlockEntry <= LastBlockEntry));
> -  } while (RegionLength != 0);
> -
> -  return EFI_SUCCESS;
> +  return UpdateRegionMappingRec (RegionStart, RegionStart + RegionSize,
> +           AttributeSetMask, AttributeClearMask, ArmGetTTBR0BaseAddress (),
> +           RootTableLevel);
>  }
>  
>  STATIC
> @@ -398,7 +303,6 @@ FillTranslationTable (
>    )
>  {
>    return UpdateRegionMapping (
> -           RootTable,
>             MemoryRegion->VirtualBase,
>             MemoryRegion->Length,
>             ArmMemoryAttributeToPageAttribute (MemoryRegion->Attributes) | TT_AF,
> @@ -455,8 +359,6 @@ ArmSetMemoryAttributes (
>    IN UINT64                    Attributes
>    )
>  {
> -  EFI_STATUS                   Status;
> -  UINT64                      *TranslationTable;
>    UINT64                       PageAttributes;
>    UINT64                       PageAttributeMask;
>  
> @@ -473,19 +375,11 @@ ArmSetMemoryAttributes (
>                            TT_PXN_MASK | TT_XN_MASK);
>    }
>  
> -  TranslationTable = ArmGetTTBR0BaseAddress ();
> -
> -  Status = UpdateRegionMapping (
> -             TranslationTable,
> +  return UpdateRegionMapping (
>               BaseAddress,
>               Length,
>               PageAttributes,
>               PageAttributeMask);

While making a neat and clear diff, this messes up coding style.

/
    Leif

> -  if (EFI_ERROR (Status)) {
> -    return Status;
> -  }
> -
> -  return EFI_SUCCESS;
>  }
>  
>  STATIC
> @@ -497,17 +391,7 @@ SetMemoryRegionAttribute (
>    IN  UINT64                    BlockEntryMask
>    )
>  {
> -  EFI_STATUS                   Status;
> -  UINT64                       *RootTable;
> -
> -  RootTable = ArmGetTTBR0BaseAddress ();
> -
> -  Status = UpdateRegionMapping (RootTable, BaseAddress, Length, Attributes, BlockEntryMask);
> -  if (EFI_ERROR (Status)) {
> -    return Status;
> -  }
> -
> -  return EFI_SUCCESS;
> +  return UpdateRegionMapping (BaseAddress, Length, Attributes, BlockEntryMask);
>  }
>  
>  EFI_STATUS
> -- 
> 2.17.1
>