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>

2 files changed, 60 insertions, 41 deletions

diff --git a/OvmfPkg/IoMmuDxe/IoMmuBuffer.c b/OvmfPkg/IoMmuDxe/IoMmuBuffer.c
index 103003cae3..f8dcd5b7ec 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;

+

+    if ((ReservedMemBitmap & MemRange->BitmapMask) == MemRange->BitmapMask) {

+      // The reserved memory is exhausted. Turn to legacy allocate.

+      goto LegacyAllocateBuffer;

+    }

 

-  MemBitmap = (mReservedMemBitmap & MemRange->BitmapMask) >> MemRange->Shift;

+    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);

 }

 

@@ -366,28 +376,42 @@ 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.

  *

  * @param MapInfo       Pointer to the MAP_INFO

@@ -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:

diff --git a/OvmfPkg/IoMmuDxe/IoMmuDxe.inf b/OvmfPkg/IoMmuDxe/IoMmuDxe.inf
index 17fca52856..d08f7e59e2 100644
--- a/OvmfPkg/IoMmuDxe/IoMmuDxe.inf
+++ b/OvmfPkg/IoMmuDxe/IoMmuDxe.inf
@@ -35,6 +35,7 @@
   MemEncryptSevLib

   MemEncryptTdxLib

   MemoryAllocationLib

+  SynchronizationLib

   UefiBootServicesTableLib

   UefiDriverEntryPoint