[edk2-devel] [PATCH 1/3] UefiCpuPkg: Reduce and optimize access to attribute

["duntan" <dun.tan@intel.com>]

From: Zhou Jianfeng <jianfeng.zhou@intel.com>

This commit is to reduce and optimize access to
attribute in CpuPageTableLib.

Unreasonable writing to attribute of page table may
leads to expection.
The assembly code for C code Pnle->Bits.Present =
Attribute->Bits.Present looks like:
   and dword [rcx], 0xfffffffe
   and eax, 0x1
   or [rcx], eax
In case Pnle->Bits.Present and Attribute->Bits.Present
is 1, Pnle->Bits.Present will be set to 0 for short
time(2 instructions) which is unexpected. If some other
core is accessing the page, it may leads to expection.
This change reduce and optimize access to attribute of
page table, attribute of page table is set only when it
need to be changed.

Signed-off-by: Zhou Jianfeng <jianfeng.zhou@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Rahul Kumar <rahul1.kumar@intel.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
---
 UefiCpuPkg/Library/CpuPageTableLib/CpuPageTableMap.c | 86 +++++++++++++++++++++++++++++++++++++++++++++++++++++---------------------------------
 1 file changed, 53 insertions(+), 33 deletions(-)

diff --git a/UefiCpuPkg/Library/CpuPageTableLib/CpuPageTableMap.c b/UefiCpuPkg/Library/CpuPageTableLib/CpuPageTableMap.c
index 36b2c4e6a3..ae4caf8dfe 100644
--- a/UefiCpuPkg/Library/CpuPageTableLib/CpuPageTableMap.c
+++ b/UefiCpuPkg/Library/CpuPageTableLib/CpuPageTableMap.c
@@ -26,52 +26,59 @@ PageTableLibSetPte4K (
   IN IA32_MAP_ATTRIBUTE  *Mask
   )
 {
+  IA32_PTE_4K  LocalPte4K;
+
+  LocalPte4K.Uint64 = Pte4K->Uint64;
   if (Mask->Bits.PageTableBaseAddressLow || Mask->Bits.PageTableBaseAddressHigh) {
-    Pte4K->Uint64 = (IA32_MAP_ATTRIBUTE_PAGE_TABLE_BASE_ADDRESS (Attribute) + Offset) | (Pte4K->Uint64 & ~IA32_PE_BASE_ADDRESS_MASK_40);
+    LocalPte4K.Uint64 = (IA32_MAP_ATTRIBUTE_PAGE_TABLE_BASE_ADDRESS (Attribute) + Offset) | (Pte4K->Uint64 & ~IA32_PE_BASE_ADDRESS_MASK_40);
   }
 
   if (Mask->Bits.Present) {
-    Pte4K->Bits.Present = Attribute->Bits.Present;
+    LocalPte4K.Bits.Present = Attribute->Bits.Present;
   }
 
   if (Mask->Bits.ReadWrite) {
-    Pte4K->Bits.ReadWrite = Attribute->Bits.ReadWrite;
+    LocalPte4K.Bits.ReadWrite = Attribute->Bits.ReadWrite;
   }
 
   if (Mask->Bits.UserSupervisor) {
-    Pte4K->Bits.UserSupervisor = Attribute->Bits.UserSupervisor;
+    LocalPte4K.Bits.UserSupervisor = Attribute->Bits.UserSupervisor;
   }
 
   if (Mask->Bits.WriteThrough) {
-    Pte4K->Bits.WriteThrough = Attribute->Bits.WriteThrough;
+    LocalPte4K.Bits.WriteThrough = Attribute->Bits.WriteThrough;
   }
 
   if (Mask->Bits.CacheDisabled) {
-    Pte4K->Bits.CacheDisabled = Attribute->Bits.CacheDisabled;
+    LocalPte4K.Bits.CacheDisabled = Attribute->Bits.CacheDisabled;
   }
 
   if (Mask->Bits.Accessed) {
-    Pte4K->Bits.Accessed = Attribute->Bits.Accessed;
+    LocalPte4K.Bits.Accessed = Attribute->Bits.Accessed;
   }
 
   if (Mask->Bits.Dirty) {
-    Pte4K->Bits.Dirty = Attribute->Bits.Dirty;
+    LocalPte4K.Bits.Dirty = Attribute->Bits.Dirty;
   }
 
   if (Mask->Bits.Pat) {
-    Pte4K->Bits.Pat = Attribute->Bits.Pat;
+    LocalPte4K.Bits.Pat = Attribute->Bits.Pat;
   }
 
   if (Mask->Bits.Global) {
-    Pte4K->Bits.Global = Attribute->Bits.Global;
+    LocalPte4K.Bits.Global = Attribute->Bits.Global;
   }
 
   if (Mask->Bits.ProtectionKey) {
-    Pte4K->Bits.ProtectionKey = Attribute->Bits.ProtectionKey;
+    LocalPte4K.Bits.ProtectionKey = Attribute->Bits.ProtectionKey;
   }
 
   if (Mask->Bits.Nx) {
-    Pte4K->Bits.Nx = Attribute->Bits.Nx;
+    LocalPte4K.Bits.Nx = Attribute->Bits.Nx;
+  }
+
+  if (Pte4K->Uint64 != LocalPte4K.Uint64) {
+    Pte4K->Uint64 = LocalPte4K.Uint64;
   }
 }
 
@@ -93,54 +100,61 @@ PageTableLibSetPleB (
   IN IA32_MAP_ATTRIBUTE                 *Mask
   )
 {
+  IA32_PAGE_LEAF_ENTRY_BIG_PAGESIZE  LocalPleB;
+
+  LocalPleB.Uint64 = PleB->Uint64;
   if (Mask->Bits.PageTableBaseAddressLow || Mask->Bits.PageTableBaseAddressHigh) {
-    PleB->Uint64 = (IA32_MAP_ATTRIBUTE_PAGE_TABLE_BASE_ADDRESS (Attribute) + Offset) | (PleB->Uint64 & ~IA32_PE_BASE_ADDRESS_MASK_39);
+    LocalPleB.Uint64 = (IA32_MAP_ATTRIBUTE_PAGE_TABLE_BASE_ADDRESS (Attribute) + Offset) | (PleB->Uint64 & ~IA32_PE_BASE_ADDRESS_MASK_39);
   }
 
-  PleB->Bits.MustBeOne = 1;
+  LocalPleB.Bits.MustBeOne = 1;
 
   if (Mask->Bits.Present) {
-    PleB->Bits.Present = Attribute->Bits.Present;
+    LocalPleB.Bits.Present = Attribute->Bits.Present;
   }
 
   if (Mask->Bits.ReadWrite) {
-    PleB->Bits.ReadWrite = Attribute->Bits.ReadWrite;
+    LocalPleB.Bits.ReadWrite = Attribute->Bits.ReadWrite;
   }
 
   if (Mask->Bits.UserSupervisor) {
-    PleB->Bits.UserSupervisor = Attribute->Bits.UserSupervisor;
+    LocalPleB.Bits.UserSupervisor = Attribute->Bits.UserSupervisor;
   }
 
   if (Mask->Bits.WriteThrough) {
-    PleB->Bits.WriteThrough = Attribute->Bits.WriteThrough;
+    LocalPleB.Bits.WriteThrough = Attribute->Bits.WriteThrough;
   }
 
   if (Mask->Bits.CacheDisabled) {
-    PleB->Bits.CacheDisabled = Attribute->Bits.CacheDisabled;
+    LocalPleB.Bits.CacheDisabled = Attribute->Bits.CacheDisabled;
   }
 
   if (Mask->Bits.Accessed) {
-    PleB->Bits.Accessed = Attribute->Bits.Accessed;
+    LocalPleB.Bits.Accessed = Attribute->Bits.Accessed;
   }
 
   if (Mask->Bits.Dirty) {
-    PleB->Bits.Dirty = Attribute->Bits.Dirty;
+    LocalPleB.Bits.Dirty = Attribute->Bits.Dirty;
   }
 
   if (Mask->Bits.Pat) {
-    PleB->Bits.Pat = Attribute->Bits.Pat;
+    LocalPleB.Bits.Pat = Attribute->Bits.Pat;
   }
 
   if (Mask->Bits.Global) {
-    PleB->Bits.Global = Attribute->Bits.Global;
+    LocalPleB.Bits.Global = Attribute->Bits.Global;
   }
 
   if (Mask->Bits.ProtectionKey) {
-    PleB->Bits.ProtectionKey = Attribute->Bits.ProtectionKey;
+    LocalPleB.Bits.ProtectionKey = Attribute->Bits.ProtectionKey;
   }
 
   if (Mask->Bits.Nx) {
-    PleB->Bits.Nx = Attribute->Bits.Nx;
+    LocalPleB.Bits.Nx = Attribute->Bits.Nx;
+  }
+
+  if (PleB->Uint64 != LocalPleB.Uint64) {
+    PleB->Uint64 = LocalPleB.Uint64;
   }
 }
 
@@ -186,24 +200,27 @@ PageTableLibSetPnle (
   IN IA32_MAP_ATTRIBUTE        *Mask
   )
 {
+  IA32_PAGE_NON_LEAF_ENTRY  LocalPnle;
+
+  LocalPnle.Uint64 = Pnle->Uint64;
   if (Mask->Bits.Present) {
-    Pnle->Bits.Present = Attribute->Bits.Present;
+    LocalPnle.Bits.Present = Attribute->Bits.Present;
   }
 
   if (Mask->Bits.ReadWrite) {
-    Pnle->Bits.ReadWrite = Attribute->Bits.ReadWrite;
+    LocalPnle.Bits.ReadWrite = Attribute->Bits.ReadWrite;
   }
 
   if (Mask->Bits.UserSupervisor) {
-    Pnle->Bits.UserSupervisor = Attribute->Bits.UserSupervisor;
+    LocalPnle.Bits.UserSupervisor = Attribute->Bits.UserSupervisor;
   }
 
   if (Mask->Bits.Nx) {
-    Pnle->Bits.Nx = Attribute->Bits.Nx;
+    LocalPnle.Bits.Nx = Attribute->Bits.Nx;
   }
 
-  Pnle->Bits.Accessed   = 0;
-  Pnle->Bits.MustBeZero = 0;
+  LocalPnle.Bits.Accessed   = 0;
+  LocalPnle.Bits.MustBeZero = 0;
 
   //
   // Set the attributes (WT, CD, A) to 0.
@@ -211,8 +228,11 @@ PageTableLibSetPnle (
   // So, it implictly requires PAT[0] is Write Back.
   // Create a new parameter if caller requires to use a different memory type for accessing page directories.
   //
-  Pnle->Bits.WriteThrough  = 0;
-  Pnle->Bits.CacheDisabled = 0;
+  LocalPnle.Bits.WriteThrough  = 0;
+  LocalPnle.Bits.CacheDisabled = 0;
+  if (Pnle->Uint64 != LocalPnle.Uint64) {
+    Pnle->Uint64 = LocalPnle.Uint64;
+  }
 }
 
 /**
-- 
2.31.1.windows.1



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