On Wed, Mar 25, 2020 at 12:38:46 +0100, Ard Biesheuvel wrote:
> Currently, depending on the size of the region being (re)mapped, the
> page table manipulation code may replace a table entry with a block entry,
> even if the existing table entry uses different mapping attributes to
> describe different parts of the region it covers. This is undesirable, and
> instead, we should avoid doing so unless we are disregarding the original
> attributes anyway. And if we make such a replacement, we should free all
> the page tables that have become orphaned in the process.
>
> So let's implement this, by taking the table entry path through the code
> for block sized regions if a table entry already exists, and the clear
> mask is set (which means we are preserving attributes from the existing
> mapping). And when we do replace a table entry with a block entry, free
> all the pages that are no longer referenced.
>
> Signed-off-by: Ard Biesheuvel <ard.biesheu...@linaro.org>
With Laszlo's Tested-by:
Reviewed-by: Leif Lindholm <l...@nuviainc.com>
> ---
> ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c | 25 ++++++++++++++++----
> 1 file changed, 21 insertions(+), 4 deletions(-)
>
> diff --git a/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c
> b/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c
> index 6f6ef5b05fbc..488156e69057 100644
> --- a/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c
> +++ b/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c
> @@ -223,8 +223,12 @@ 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) {
> + if (Level == 0 || ((RegionStart | BlockEnd) & BlockMask) != 0 ||
> + (IsTableEntry (*Entry, Level) && AttributeClearMask != 0)) {
> ASSERT (Level < 3);
>
> if (!IsTableEntry (*Entry, Level)) {
> @@ -245,6 +249,8 @@ UpdateRegionMappingRecursive (
> InvalidateDataCacheRange (TranslationTable, EFI_PAGE_SIZE);
> }
>
> + ZeroMem (TranslationTable, EFI_PAGE_SIZE);
> +
> if (IsBlockEntry (*Entry, Level)) {
> //
> // We are splitting an existing block entry, so we have to populate
> @@ -262,8 +268,6 @@ UpdateRegionMappingRecursive (
> FreePages (TranslationTable, 1);
> return Status;
> }
> - } else {
> - ZeroMem (TranslationTable, EFI_PAGE_SIZE);
> }
> } else {
> TranslationTable = (VOID *)(UINTN)(*Entry &
> TT_ADDRESS_MASK_BLOCK_ENTRY);
> @@ -300,7 +304,20 @@ UpdateRegionMappingRecursive (
> EntryValue |= (Level == 3) ? TT_TYPE_BLOCK_ENTRY_LEVEL3
> : TT_TYPE_BLOCK_ENTRY;
>
> - ReplaceTableEntry (Entry, EntryValue, RegionStart, FALSE);
> + 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);
> + } else {
> + ReplaceTableEntry (Entry, EntryValue, RegionStart, FALSE);
> + }
> }
> }
> return EFI_SUCCESS;
> --
> 2.17.1
>
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