ArmPkg/ArmMmuLib ARM: Split off XN page descriptor bit from type field

With large page support out of the picture, we can treat bits 1 and 0 of
the page descriptor as individual valid and XN bits, instead of treating
XN as a page type. Doing so aligns the handling of the attribute with
the section descriptor layout, as well as the XN handling on AArch64,
and this is beneficial for maintainability.

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

1 files changed, 6 insertions, 6 deletions

diff --git a/ArmPkg/Library/ArmMmuLib/Arm/ArmMmuLibUpdate.c b/ArmPkg/Library/ArmMmuLib/Arm/ArmMmuLibUpdate.c
index 9ca00c976d..12d0f4c30f 100644
--- a/ArmPkg/Library/ArmMmuLib/Arm/ArmMmuLibUpdate.c
+++ b/ArmPkg/Library/ArmMmuLib/Arm/ArmMmuLibUpdate.c
@@ -104,12 +104,8 @@ UpdatePageEntries (
 

   // EntryMask: bitmask of values to change (1 = change this value, 0 = leave alone)

   // EntryValue: values at bit positions specified by EntryMask

-  EntryMask = TT_DESCRIPTOR_PAGE_TYPE_MASK | TT_DESCRIPTOR_PAGE_AP_MASK;

-  if ((Attributes & EFI_MEMORY_XP) != 0) {

-    EntryValue = TT_DESCRIPTOR_PAGE_TYPE_PAGE_XN;

-  } else {

-    EntryValue = TT_DESCRIPTOR_PAGE_TYPE_PAGE;

-  }

+  EntryMask = TT_DESCRIPTOR_PAGE_TYPE_MASK | TT_DESCRIPTOR_PAGE_AP_MASK | TT_DESCRIPTOR_PAGE_XN_MASK;

+  EntryValue = TT_DESCRIPTOR_PAGE_TYPE_PAGE;

 

   // Although the PI spec is unclear on this, the GCD guarantees that only

   // one Attribute bit is set at a time, so the order of the conditionals below

@@ -148,6 +144,10 @@ UpdatePageEntries (
     EntryValue |= TT_DESCRIPTOR_PAGE_AP_RW_RW;

   }

 

+  if ((Attributes & EFI_MEMORY_XP) != 0) {

+    EntryValue |= TT_DESCRIPTOR_PAGE_XN_MASK;

+  }

+

   // Obtain page table base

   FirstLevelTable = (ARM_FIRST_LEVEL_DESCRIPTOR *)ArmGetTTBR0BaseAddress ();