> v3:
>    Create driver's own page table pool instead of inheriting from DxeIpl.

> v2:
>    Use the page table pool to allocate new page tables and save code
>    to enable protection for them separately.

One of the functionalities of CpuDxe is to update memory paging attributes.
If page table protection is applied, it must be disabled temporarily before
any attributes update and enabled again afterwards.

This patch makes use of the same way as DxeIpl to allocate page table memory
from reserved memory pool, which helps to reduce potential "split" operation
and recursive calling of SetMemorySpaceAttributes().

Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Jian J Wang <jian.j.wang@intel.com>
---
 UefiCpuPkg/CpuDxe/CpuDxe.c       |  17 ++-
 UefiCpuPkg/CpuDxe/CpuDxe.h       |   2 +
 UefiCpuPkg/CpuDxe/CpuPageTable.c | 226 +++++++++++++++++++++++++++++++++++++--
 UefiCpuPkg/CpuDxe/CpuPageTable.h |  34 ++++++
 4 files changed, 270 insertions(+), 9 deletions(-)

diff --git a/UefiCpuPkg/CpuDxe/CpuDxe.c b/UefiCpuPkg/CpuDxe/CpuDxe.c
index 8ddebabd02..6ae2dcd1c7 100644
--- a/UefiCpuPkg/CpuDxe/CpuDxe.c
+++ b/UefiCpuPkg/CpuDxe/CpuDxe.c
@@ -25,6 +25,7 @@
 BOOLEAN                   InterruptState = FALSE;
 EFI_HANDLE                mCpuHandle = NULL;
 BOOLEAN                   mIsFlushingGCD;
+BOOLEAN                   mIsAllocatingPageTable = FALSE;
 UINT64                    mValidMtrrAddressMask;
 UINT64                    mValidMtrrBitsMask;
 UINT64                    mTimerPeriod = 0;
@@ -407,6 +408,20 @@ CpuSetMemoryAttributes (
     return EFI_SUCCESS;
   }
 
+  //
+  // During memory attributes updating, new pages may be allocated to setup
+  // smaller granularity of page table. Page allocation action might then cause
+  // another calling of CpuSetMemoryAttributes() recursively, due to memory
+  // protection policy configured (such as PcdDxeNxMemoryProtectionPolicy).
+  // Since this driver will always protect memory used as page table by itself,
+  // there's no need to apply protection policy requested from memory service.
+  // So it's safe to just return EFI_SUCCESS if this time of calling is caused
+  // by page table memory allocation.
+  //
+  if (mIsAllocatingPageTable) {
+    DEBUG((DEBUG_VERBOSE, "  Allocating page table memory\n"));
+    return EFI_SUCCESS;
+  }
 
   CacheAttributes = Attributes & CACHE_ATTRIBUTE_MASK;
   MemoryAttributes = Attributes & MEMORY_ATTRIBUTE_MASK;
@@ -487,7 +502,7 @@ CpuSetMemoryAttributes (
   //
   // Set memory attribute by page table
   //
-  return AssignMemoryPageAttributes (NULL, BaseAddress, Length, MemoryAttributes, AllocatePages);
+  return AssignMemoryPageAttributes (NULL, BaseAddress, Length, MemoryAttributes, NULL);
 }
 
 /**
diff --git a/UefiCpuPkg/CpuDxe/CpuDxe.h b/UefiCpuPkg/CpuDxe/CpuDxe.h
index 9c0d22359d..540f5f2dbf 100644
--- a/UefiCpuPkg/CpuDxe/CpuDxe.h
+++ b/UefiCpuPkg/CpuDxe/CpuDxe.h
@@ -273,5 +273,7 @@ RefreshGcdMemoryAttributesFromPaging (
   VOID
   );
 
+extern BOOLEAN mIsAllocatingPageTable;
+
 #endif
 
diff --git a/UefiCpuPkg/CpuDxe/CpuPageTable.c b/UefiCpuPkg/CpuDxe/CpuPageTable.c
index 9658ed74c5..57ec76378a 100644
--- a/UefiCpuPkg/CpuDxe/CpuPageTable.c
+++ b/UefiCpuPkg/CpuDxe/CpuPageTable.c
@@ -87,6 +87,8 @@ PAGE_ATTRIBUTE_TABLE mPageAttributeTable[] = {
   {Page1G,  SIZE_1GB, PAGING_1G_ADDRESS_MASK_64},
 };
 
+PAGE_TABLE_POOL   *mPageTablePool = NULL;
+
 /**
   Enable write protection function for AP.
 
@@ -172,10 +174,6 @@ GetCurrentPagingContext (
   }
   if ((AsmReadCr0 () & BIT31) != 0) {
     PagingContext->ContextData.X64.PageTableBase = (AsmReadCr3 () & PAGING_4K_ADDRESS_MASK_64);
-    if ((AsmReadCr0 () & BIT16) == 0) {
-      AsmWriteCr0 (AsmReadCr0 () | BIT16);
-      SyncMemoryPageAttributesAp (SyncCpuEnableWriteProtection);
-    }
   } else {
     PagingContext->ContextData.X64.PageTableBase = 0;
   }
@@ -561,6 +559,59 @@ SplitPage (
   }
 }
 
+/**
+ Check the WP status in CR0 register. This bit is used to lock or unlock write
+ access to pages marked as read-only.
+
+  @retval TRUE    Write protection is enabled.
+  @retval FALSE   Write protection is disabled.
+**/
+BOOLEAN
+IsReadOnlyPageWriteProtected (
+  VOID
+  )
+{
+  return ((AsmReadCr0 () & BIT16) != 0);
+}
+
+/**
+  Disable write protection function for AP.
+
+  @param[in,out] Buffer  The pointer to private data buffer.
+**/
+VOID
+EFIAPI
+SyncCpuDisableWriteProtection (
+  IN OUT VOID *Buffer
+  )
+{
+  AsmWriteCr0 (AsmReadCr0() & ~BIT16);
+}
+
+/**
+ Disable Write Protect on pages marked as read-only.
+**/
+VOID
+DisableReadOnlyPageWriteProtect (
+  VOID
+  )
+{
+  AsmWriteCr0 (AsmReadCr0() & ~BIT16);
+  SyncMemoryPageAttributesAp (SyncCpuDisableWriteProtection);
+}
+
+/**
+ Enable Write Protect on pages marked as read-only.
+**/
+VOID
+EnableReadOnlyPageWriteProtect (
+  VOID
+  )
+{
+  AsmWriteCr0 (AsmReadCr0() | BIT16);
+  SyncMemoryPageAttributesAp (SyncCpuEnableWriteProtection);
+}
+
 /**
   This function modifies the page attributes for the memory region specified by BaseAddress and
   Length from their current attributes to the attributes specified by Attributes.
@@ -609,6 +660,7 @@ ConvertMemoryPageAttributes (
   PAGE_ATTRIBUTE                    SplitAttribute;
   RETURN_STATUS                     Status;
   BOOLEAN                           IsEntryModified;
+  BOOLEAN                           IsWpEnabled;
 
   if ((BaseAddress & (SIZE_4KB - 1)) != 0) {
     DEBUG ((DEBUG_ERROR, "BaseAddress(0x%lx) is not aligned!\n", BaseAddress));
@@ -665,14 +717,27 @@ ConvertMemoryPageAttributes (
   if (IsModified != NULL) {
     *IsModified = FALSE;
   }
+  if (AllocatePagesFunc == NULL) {
+    AllocatePagesFunc = AllocatePageTableMemory;
+  }
+
+  //
+  // Make sure that the page table is changeable.
+  //
+  IsWpEnabled = IsReadOnlyPageWriteProtected ();
+  if (IsWpEnabled) {
+    DisableReadOnlyPageWriteProtect ();
+  }
 
   //
   // Below logic is to check 2M/4K page to make sure we donot waist memory.
   //
+  Status = EFI_SUCCESS;
   while (Length != 0) {
     PageEntry = GetPageTableEntry (&CurrentPagingContext, BaseAddress, &PageAttribute);
     if (PageEntry == NULL) {
-      return RETURN_UNSUPPORTED;
+      Status = RETURN_UNSUPPORTED;
+      goto Done;
     }
     PageEntryLength = PageAttributeToLength (PageAttribute);
     SplitAttribute = NeedSplitPage (BaseAddress, Length, PageEntry, PageAttribute);
@@ -690,11 +755,13 @@ ConvertMemoryPageAttributes (
       Length -= PageEntryLength;
     } else {
       if (AllocatePagesFunc == NULL) {
-        return RETURN_UNSUPPORTED;
+        Status = RETURN_UNSUPPORTED;
+        goto Done;
       }
       Status = SplitPage (PageEntry, PageAttribute, SplitAttribute, AllocatePagesFunc);
       if (RETURN_ERROR (Status)) {
-        return RETURN_UNSUPPORTED;
+        Status = RETURN_UNSUPPORTED;
+        goto Done;
       }
       if (IsSplitted != NULL) {
         *IsSplitted = TRUE;
@@ -709,7 +776,14 @@ ConvertMemoryPageAttributes (
     }
   }
 
-  return RETURN_SUCCESS;
+Done:
+  //
+  // Restore page table write protection, if any.
+  //
+  if (IsWpEnabled) {
+    EnableReadOnlyPageWriteProtect ();
+  }
+  return Status;
 }
 
 /**
@@ -922,6 +996,130 @@ RefreshGcdMemoryAttributesFromPaging (
   FreePool (MemorySpaceMap);
 }
 
+/**
+  Initialize a buffer pool for page table use only.
+
+  To reduce the potential split operation on page table, the pages reserved for
+  page table should be allocated in the times of 512 (= SIZE_2MB) and at the
+  boundary of SIZE_2MB. So the page pool is always initialized with number of
+  pages greater than or equal to the given PoolPages.
+
+  Once the pages in the pool are used up, this method should be called again to
+  reserve at least another 512 pages. Usually this won't happen often in
+  practice.
+
+  @param[in] PoolPages      The least page number of the pool to be created.
+
+  @retval TRUE    The pool is initialized successfully.
+  @retval FALSE   The memory is out of resource.
+**/
+BOOLEAN
+InitializePageTablePool (
+  IN  UINTN                           PoolPages
+  )
+{
+  VOID                      *Buffer;
+  BOOLEAN                   IsModified;
+
+  //
+  // Always reserve at least PAGE_TABLE_POOL_UNIT_PAGES (512).
+  //
+  if (PoolPages <= PAGE_TABLE_POOL_UNIT_PAGES) {
+    PoolPages = PAGE_TABLE_POOL_UNIT_PAGES;
+  } else {
+    PoolPages = ((PoolPages + PAGE_TABLE_POOL_UNIT_PAGES) %
+                 PAGE_TABLE_POOL_UNIT_PAGES) * PAGE_TABLE_POOL_UNIT_PAGES;
+  }
+
+  Buffer = AllocateAlignedPages (PoolPages, PAGE_TABLE_POOL_ALIGNMENT);
+  if (Buffer == NULL) {
+    DEBUG ((DEBUG_ERROR, "ERROR: Out of aligned pages\r\n"));
+    return FALSE;
+  }
+
+  //
+  // Link all pools into a list for easier track later.
+  //
+  if (mPageTablePool == NULL) {
+    mPageTablePool = Buffer;
+    mPageTablePool->NextPool = mPageTablePool;
+  } else {
+    ((PAGE_TABLE_POOL *)Buffer)->NextPool = mPageTablePool->NextPool;
+    mPageTablePool->NextPool = Buffer;
+    mPageTablePool = Buffer;
+  }
+
+  //
+  // Reserve one page for pool header.
+  //
+  mPageTablePool->FreePages  = PoolPages - 1;
+  mPageTablePool->Offset = EFI_PAGES_TO_SIZE (1);
+
+  //
+  // Mark the whole pool pages as read-only.
+  //
+  ConvertMemoryPageAttributes (
+    NULL,
+    (PHYSICAL_ADDRESS)(UINTN)Buffer,
+    EFI_PAGES_TO_SIZE (PoolPages),
+    EFI_MEMORY_RO,
+    PageActionSet,
+    AllocatePageTableMemory,
+    NULL,
+    &IsModified
+    );
+  ASSERT (IsModified == TRUE);
+
+  return TRUE;
+}
+
+/**
+  This API provides a way to allocate memory for page table.
+
+  This API can be called more than once to allocate memory for page tables.
+
+  Allocates the number of 4KB pages and returns a pointer to the allocated
+  buffer. The buffer returned is aligned on a 4KB boundary.
+
+  If Pages is 0, then NULL is returned.
+  If there is not enough memory remaining to satisfy the request, then NULL is
+  returned.
+
+  @param  Pages                 The number of 4 KB pages to allocate.
+
+  @return A pointer to the allocated buffer or NULL if allocation fails.
+
+**/
+VOID *
+EFIAPI
+AllocatePageTableMemory (
+  IN UINTN           Pages
+  )
+{
+  VOID                            *Buffer;
+
+  if (Pages == 0) {
+    return NULL;
+  }
+
+  //
+  // Renew the pool if necessary.
+  //
+  if (mPageTablePool == NULL ||
+      Pages > mPageTablePool->FreePages) {
+    if (!InitializePageTablePool (Pages)) {
+      return NULL;
+    }
+  }
+
+  Buffer = (UINT8 *)mPageTablePool + mPageTablePool->Offset;
+
+  mPageTablePool->Offset     += EFI_PAGES_TO_SIZE (Pages);
+  mPageTablePool->FreePages  -= Pages;
+
+  return Buffer;
+}
+
 /**
   Initialize the Page Table lib.
 **/
@@ -933,6 +1131,18 @@ InitializePageTableLib (
   PAGE_TABLE_LIB_PAGING_CONTEXT     CurrentPagingContext;
 
   GetCurrentPagingContext (&CurrentPagingContext);
+
+  //
+  // Reserve memory of page tables for future uses, if paging is enabled.
+  //
+  if (CurrentPagingContext.ContextData.X64.PageTableBase != 0 &&
+      (CurrentPagingContext.ContextData.Ia32.Attributes &
+       PAGE_TABLE_LIB_PAGING_CONTEXT_IA32_X64_ATTRIBUTES_PAE) != 0) {
+    DisableReadOnlyPageWriteProtect ();
+    InitializePageTablePool (PAGE_TABLE_POOL_UNIT_SIZE);
+    EnableReadOnlyPageWriteProtect ();
+  }
+
   DEBUG ((DEBUG_INFO, "CurrentPagingContext:\n", CurrentPagingContext.MachineType));
   DEBUG ((DEBUG_INFO, "  MachineType   - 0x%x\n", CurrentPagingContext.MachineType));
   DEBUG ((DEBUG_INFO, "  PageTableBase - 0x%x\n", CurrentPagingContext.ContextData.X64.PageTableBase));
diff --git a/UefiCpuPkg/CpuDxe/CpuPageTable.h b/UefiCpuPkg/CpuDxe/CpuPageTable.h
index eaff595b4c..2557ffaecf 100644
--- a/UefiCpuPkg/CpuDxe/CpuPageTable.h
+++ b/UefiCpuPkg/CpuDxe/CpuPageTable.h
@@ -50,6 +50,19 @@ typedef struct {
   PAGE_TABLE_LIB_PAGING_CONTEXT_DATA     ContextData;
 } PAGE_TABLE_LIB_PAGING_CONTEXT;
 
+#define PAGE_TABLE_POOL_ALIGNMENT   BASE_2MB
+#define PAGE_TABLE_POOL_UNIT_SIZE   SIZE_2MB
+#define PAGE_TABLE_POOL_UNIT_PAGES  EFI_SIZE_TO_PAGES (SIZE_2MB)
+#define PAGE_TABLE_POOL_ALIGN_MASK  \
+  (~(EFI_PHYSICAL_ADDRESS)(PAGE_TABLE_POOL_ALIGNMENT - 1))
+
+typedef struct {
+  VOID            *NextPool;
+  UINTN           Offset;
+  UINTN           FreePages;
+} PAGE_TABLE_POOL;
+
+
 /**
   Allocates one or more 4KB pages for page table.
 
@@ -110,4 +123,25 @@ InitializePageTableLib (
   VOID
   );
 
+/**
+  This API provides a way to allocate memory for page table.
+
+  This API can be called more once to allocate memory for page tables.
+
+  Allocates the number of 4KB pages of type EfiRuntimeServicesData and returns a pointer to the
+  allocated buffer.  The buffer returned is aligned on a 4KB boundary.  If Pages is 0, then NULL
+  is returned.  If there is not enough memory remaining to satisfy the request, then NULL is
+  returned.
+
+  @param  Pages                 The number of 4 KB pages to allocate.
+
+  @return A pointer to the allocated buffer or NULL if allocation fails.
+
+**/
+VOID *
+EFIAPI
+AllocatePageTableMemory (
+  IN UINTN           Pages
+  );
+
 #endif
-- 
2.15.1.windows.2

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