edk2/0017-OvmfPkg-IoMmuDxe-don-t-rely-on-TPLs-to-manage-concur.patch

From bf2f6173802c709a84c36d43f414c815ad6aa2f6 Mon Sep 17 00:00:00 2001
From: Ard Biesheuvel <ardb@kernel.org>
Date: Thu, 20 Jul 2023 15:45:57 +0200
Subject: [PATCH 17/20] OvmfPkg/IoMmuDxe: don't rely on TPLs to manage
 concurrency

Instead of relying on raising the TPL to protect the critical sections
that manipulate the global bitmask that keeps track of bounce buffer
allocations, use compare-and-exchange to manage the global variable, and
tweak the logic to line up with that.

Given that IoMmuDxe implements a singleton protocol that is shared
between multiple drivers, and considering the elaborate and confusing
requirements in the UEFP spec regarding TPL levels at which protocol
methods may be invoked, not relying on TPL levels at all is a more
robust approach in this case.

Link: https://bugzilla.redhat.com/show_bug.cgi?id=2211060
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Pedro Falcato <pedro.falcato@gmail.com>
(cherry picked from commit dfb941d32a2f38c9177729e39c6a6515abbbad48)
---
 OvmfPkg/IoMmuDxe/IoMmuDxe.inf  |   1 +
 OvmfPkg/IoMmuDxe/IoMmuBuffer.c | 100 +++++++++++++++++++--------------
 2 files changed, 60 insertions(+), 41 deletions(-)

diff --git a/OvmfPkg/IoMmuDxe/IoMmuDxe.inf b/OvmfPkg/IoMmuDxe/IoMmuDxe.inf
index 17fca5285692..d08f7e59e2b6 100644
--- a/OvmfPkg/IoMmuDxe/IoMmuDxe.inf
+++ b/OvmfPkg/IoMmuDxe/IoMmuDxe.inf
@@ -35,6 +35,7 @@ [LibraryClasses]
   MemEncryptSevLib
   MemEncryptTdxLib
   MemoryAllocationLib
+  SynchronizationLib
   UefiBootServicesTableLib
   UefiDriverEntryPoint
 
diff --git a/OvmfPkg/IoMmuDxe/IoMmuBuffer.c b/OvmfPkg/IoMmuDxe/IoMmuBuffer.c
index 103003cae376..f8dcd5b7ec92 100644
--- a/OvmfPkg/IoMmuDxe/IoMmuBuffer.c
+++ b/OvmfPkg/IoMmuDxe/IoMmuBuffer.c
@@ -12,6 +12,7 @@
 #include <Library/MemEncryptSevLib.h>
 #include <Library/MemEncryptTdxLib.h>
 #include <Library/PcdLib.h>
+#include <Library/SynchronizationLib.h>
 #include <Library/UefiBootServicesTableLib.h>
 #include "IoMmuInternal.h"
 
@@ -268,16 +269,17 @@ InternalAllocateBuffer (
   IN  EFI_ALLOCATE_TYPE        Type,
   IN  EFI_MEMORY_TYPE          MemoryType,
   IN  UINTN                    Pages,
-  IN OUT UINT32                *ReservedMemBitmap,
+  OUT UINT32                   *ReservedMemBit,
   IN OUT EFI_PHYSICAL_ADDRESS  *PhysicalAddress
   )
 {
   UINT32                    MemBitmap;
+  UINT32                    ReservedMemBitmap;
   UINT8                     Index;
   IOMMU_RESERVED_MEM_RANGE  *MemRange;
   UINTN                     PagesOfLastMemRange;
 
-  *ReservedMemBitmap = 0;
+  *ReservedMemBit = 0;
 
   if (Pages == 0) {
     ASSERT (FALSE);
@@ -309,23 +311,31 @@ InternalAllocateBuffer (
 
   MemRange = &mReservedMemRanges[Index];
 
-  if ((mReservedMemBitmap & MemRange->BitmapMask) == MemRange->BitmapMask) {
-    // The reserved memory is exausted. Turn to legacy allocate.
-    goto LegacyAllocateBuffer;
-  }
+  do {
+    ReservedMemBitmap = mReservedMemBitmap;
 
-  MemBitmap = (mReservedMemBitmap & MemRange->BitmapMask) >> MemRange->Shift;
+    if ((ReservedMemBitmap & MemRange->BitmapMask) == MemRange->BitmapMask) {
+      // The reserved memory is exhausted. Turn to legacy allocate.
+      goto LegacyAllocateBuffer;
+    }
+
+    MemBitmap = (ReservedMemBitmap & MemRange->BitmapMask) >> MemRange->Shift;
 
-  for (Index = 0; Index < MemRange->Slots; Index++) {
-    if ((MemBitmap & (UINT8)(1<<Index)) == 0) {
-      break;
+    for (Index = 0; Index < MemRange->Slots; Index++) {
+      if ((MemBitmap & (UINT8)(1<<Index)) == 0) {
+        break;
+      }
     }
-  }
 
-  ASSERT (Index != MemRange->Slots);
+    ASSERT (Index != MemRange->Slots);
 
-  *PhysicalAddress   = MemRange->StartAddressOfMemRange + Index * SIZE_OF_MEM_RANGE (MemRange) + MemRange->HeaderSize;
-  *ReservedMemBitmap = (UINT32)(1 << (Index + MemRange->Shift));
+    *PhysicalAddress = MemRange->StartAddressOfMemRange + Index * SIZE_OF_MEM_RANGE (MemRange) + MemRange->HeaderSize;
+    *ReservedMemBit  = (UINT32)(1 << (Index + MemRange->Shift));
+  } while (ReservedMemBitmap != InterlockedCompareExchange32 (
+                                  &mReservedMemBitmap,
+                                  ReservedMemBitmap,
+                                  ReservedMemBitmap | *ReservedMemBit
+                                  ));
 
   DEBUG ((
     DEBUG_VERBOSE,
@@ -334,16 +344,16 @@ InternalAllocateBuffer (
     MemRange->DataSize,
     *PhysicalAddress,
     Pages,
-    *ReservedMemBitmap,
-    mReservedMemBitmap,
-    mReservedMemBitmap | *ReservedMemBitmap
+    *ReservedMemBit,
+    ReservedMemBitmap,
+    ReservedMemBitmap | *ReservedMemBit
     ));
 
   return EFI_SUCCESS;
 
 LegacyAllocateBuffer:
 
-  *ReservedMemBitmap = 0;
+  *ReservedMemBit = 0;
   return gBS->AllocatePages (Type, MemoryType, Pages, PhysicalAddress);
 }
 
@@ -366,27 +376,41 @@ IoMmuAllocateBounceBuffer (
   )
 {
   EFI_STATUS  Status;
-  UINT32      ReservedMemBitmap;
-  EFI_TPL     OldTpl;
-
-  OldTpl            = gBS->RaiseTPL (TPL_NOTIFY);
-  ReservedMemBitmap = 0;
-  Status            = InternalAllocateBuffer (
-                        Type,
-                        MemoryType,
-                        MapInfo->NumberOfPages,
-                        &ReservedMemBitmap,
-                        &MapInfo->PlainTextAddress
-                        );
-  MapInfo->ReservedMemBitmap = ReservedMemBitmap;
-  mReservedMemBitmap        |= ReservedMemBitmap;
-  gBS->RestoreTPL (OldTpl);
 
+  Status = InternalAllocateBuffer (
+             Type,
+             MemoryType,
+             MapInfo->NumberOfPages,
+             &MapInfo->ReservedMemBitmap,
+             &MapInfo->PlainTextAddress
+             );
   ASSERT (Status == EFI_SUCCESS);
 
   return Status;
 }
 
+/**
+ * Clear a bit in the reserved memory bitmap in a thread safe manner
+ *
+ * @param ReservedMemBit  The bit to clear
+ */
+STATIC
+VOID
+ClearReservedMemBit (
+  IN  UINT32  ReservedMemBit
+  )
+{
+  UINT32  ReservedMemBitmap;
+
+  do {
+    ReservedMemBitmap = mReservedMemBitmap;
+  } while (ReservedMemBitmap != InterlockedCompareExchange32 (
+                                  &mReservedMemBitmap,
+                                  ReservedMemBitmap,
+                                  ReservedMemBitmap & ~ReservedMemBit
+                                  ));
+}
+
 /**
  * Free the bounce buffer allocated in IoMmuAllocateBounceBuffer.
  *
@@ -398,8 +422,6 @@ IoMmuFreeBounceBuffer (
   IN OUT     MAP_INFO  *MapInfo
   )
 {
-  EFI_TPL  OldTpl;
-
   if (MapInfo->ReservedMemBitmap == 0) {
     gBS->FreePages (MapInfo->PlainTextAddress, MapInfo->NumberOfPages);
   } else {
@@ -412,11 +434,9 @@ IoMmuFreeBounceBuffer (
       mReservedMemBitmap,
       mReservedMemBitmap & ((UINT32)(~MapInfo->ReservedMemBitmap))
       ));
-    OldTpl                     = gBS->RaiseTPL (TPL_NOTIFY);
+    ClearReservedMemBit (MapInfo->ReservedMemBitmap);
     MapInfo->PlainTextAddress  = 0;
-    mReservedMemBitmap        &= (UINT32)(~MapInfo->ReservedMemBitmap);
     MapInfo->ReservedMemBitmap = 0;
-    gBS->RestoreTPL (OldTpl);
   }
 
   return EFI_SUCCESS;
@@ -452,8 +472,6 @@ IoMmuAllocateCommonBuffer (
              );
   ASSERT (Status == EFI_SUCCESS);
 
-  mReservedMemBitmap |= *ReservedMemBitmap;
-
   if (*ReservedMemBitmap != 0) {
     *PhysicalAddress -= SIZE_4KB;
   }
@@ -494,7 +512,7 @@ IoMmuFreeCommonBuffer (
     mReservedMemBitmap & ((UINT32)(~CommonBufferHeader->ReservedMemBitmap))
     ));
 
-  mReservedMemBitmap &= (UINT32)(~CommonBufferHeader->ReservedMemBitmap);
+  ClearReservedMemBit (CommonBufferHeader->ReservedMemBitmap);
   return EFI_SUCCESS;
 
 LegacyFreeCommonBuffer:
-- 
2.41.0