[edk2-devel] [PATCH v2 4/9] ArmPkg/ArmMmuLib ARM: cache-invalidate initial page table entries

[Ard Biesheuvel]

In the ARM version of ArmMmuLib, we are currently relying on set/way
invalidation to ensure that the caches are in a consistent state with
respect to main memory once we turn the MMU on. Even if set/way
operations were the appropriate method to achieve this, doing an
invalidate-all first and then populating the page table entries creates
a window where page table entries could be loaded speculatively into
the caches before we modify them, and shadow the new values that we
write there.

So let's get rid of the blanket clean/invalidate operations, and instead,
invalidate each section entry before and after it is updated (to address
all the little corner cases that the ARMv7 spec permits), and invalidate
sets of level 2 entries in blocks, using the generic invalidation routine
from CacheMaintenanceLib

On ARMv7, cache maintenance may be required also when the MMU is
enabled, in case the page table walker is not cache coherent. However,
the code being updated here is guaranteed to run only when the MMU is
still off, and so we can disregard the case when the MMU and caches
are on.

Since the MMU and D-cache are already off when we reach this point, we
can drop the MMU and D-cache disables as well. Maintenance of the I-cache
is unnecessary, since we are not modifying any code, and the installed
mapping is guaranteed to be 1:1. This means we can also leave it enabled
while the page table population code is running.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
---
 ArmPkg/Library/ArmMmuLib/Arm/ArmMmuLibCore.c | 55 +++++++++++++++-----
 1 file changed, 41 insertions(+), 14 deletions(-)

diff --git a/ArmPkg/Library/ArmMmuLib/Arm/ArmMmuLibCore.c b/ArmPkg/Library/ArmMmuLib/Arm/ArmMmuLibCore.c
index aca7a37facac..7c7cad2c3d9d 100644
--- a/ArmPkg/Library/ArmMmuLib/Arm/ArmMmuLibCore.c
+++ b/ArmPkg/Library/ArmMmuLib/Arm/ArmMmuLibCore.c
@@ -178,11 +178,25 @@ PopulateLevel2PageTable (
 
   ASSERT (FirstPageOffset + Pages <= TRANSLATION_TABLE_PAGE_COUNT);
 
+  //
+  // Invalidate once to prevent page table updates to hit in the
+  // caches inadvertently.
+  //
+  InvalidateDataCacheRange ((UINT32 *)TranslationTable + FirstPageOffset,
+    RemainLength / TT_DESCRIPTOR_PAGE_SIZE * sizeof (*PageEntry));
+
   for (Index = 0; Index < Pages; Index++) {
     *PageEntry++     =  TT_DESCRIPTOR_PAGE_BASE_ADDRESS(PhysicalBase) | PageAttributes;
     PhysicalBase += TT_DESCRIPTOR_PAGE_SIZE;
   }
 
+  //
+  // Invalidate again to ensure that any line fetches that may have occurred
+  // [speculatively] since the previous invalidate are evicted again.
+  //
+  ArmDataMemoryBarrier ();
+  InvalidateDataCacheRange ((UINT32 *)TranslationTable + FirstPageOffset,
+    RemainLength / TT_DESCRIPTOR_PAGE_SIZE * sizeof (*PageEntry));
 }
 
 STATIC
@@ -253,11 +267,28 @@ FillTranslationTable (
   SectionEntry    = TRANSLATION_TABLE_ENTRY_FOR_VIRTUAL_ADDRESS(TranslationTable, MemoryRegion->VirtualBase);
 
   while (RemainLength != 0) {
+    //
+    // Ensure that the assignment of the page table entry will not hit
+    // in the cache. Whether this could occur is IMPLEMENTATION DEFINED
+    // and thus permitted by the ARMv7 architecture.
+    //
+    ArmInvalidateDataCacheEntryByMVA ((UINTN)SectionEntry);
+    ArmDataSynchronizationBarrier ();
+
     if (PhysicalBase % TT_DESCRIPTOR_SECTION_SIZE == 0 &&
         RemainLength >= TT_DESCRIPTOR_SECTION_SIZE) {
       // Case: Physical address aligned on the Section Size (1MB) && the length
       // is greater than the Section Size
-      *SectionEntry++ = TT_DESCRIPTOR_SECTION_BASE_ADDRESS(PhysicalBase) | Attributes;
+      *SectionEntry = TT_DESCRIPTOR_SECTION_BASE_ADDRESS(PhysicalBase) | Attributes;
+
+      //
+      // Issue a DMB to ensure that the page table entry update made it to
+      // memory before we issue the invalidate, otherwise, a subsequent
+      // speculative fetch could observe the old value.
+      //
+      ArmDataMemoryBarrier ();
+      ArmInvalidateDataCacheEntryByMVA ((UINTN)SectionEntry++);
+
       PhysicalBase += TT_DESCRIPTOR_SECTION_SIZE;
       RemainLength -= TT_DESCRIPTOR_SECTION_SIZE;
     } else {
@@ -267,9 +298,17 @@ FillTranslationTable (
       // Case: Physical address aligned on the Section Size (1MB) && the length
       //       does not fill a section
       // Case: Physical address NOT aligned on the Section Size (1MB)
-      PopulateLevel2PageTable (SectionEntry++, PhysicalBase, PageMapLength,
+      PopulateLevel2PageTable (SectionEntry, PhysicalBase, PageMapLength,
         MemoryRegion->Attributes);
 
+      //
+      // Issue a DMB to ensure that the page table entry update made it to
+      // memory before we issue the invalidate, otherwise, a subsequent
+      // speculative fetch could observe the old value.
+      //
+      ArmDataMemoryBarrier ();
+      ArmInvalidateDataCacheEntryByMVA ((UINTN)SectionEntry++);
+
       // If it is the last entry
       if (RemainLength < TT_DESCRIPTOR_SECTION_SIZE) {
         break;
@@ -349,18 +388,6 @@ ArmConfigureMmu (
     }
   }
 
-  ArmCleanInvalidateDataCache ();
-  ArmInvalidateInstructionCache ();
-
-  ArmDisableDataCache ();
-  ArmDisableInstructionCache();
-  // TLBs are also invalidated when calling ArmDisableMmu()
-  ArmDisableMmu ();
-
-  // Make sure nothing sneaked into the cache
-  ArmCleanInvalidateDataCache ();
-  ArmInvalidateInstructionCache ();
-
   ArmSetTTBR0 ((VOID *)(UINTN)(((UINTN)TranslationTable & ~TRANSLATION_TABLE_SECTION_ALIGNMENT_MASK) | (TTBRAttributes & 0x7F)));
 
   //
-- 
2.17.1


-=-=-=-=-=-=-=-=-=-=-=-
Groups.io Links: You receive all messages sent to this group.

View/Reply Online (#55434): https://edk2.groups.io/g/devel/message/55434
Mute This Topic: https://groups.io/mt/71732159/1813853
Group Owner: devel+owner at edk2.groups.io
Unsubscribe: https://edk2.groups.io/g/devel/unsub  [edk2-devel-archive at redhat.com]
-=-=-=-=-=-=-=-=-=-=-=-