Recognize an extended TSEG when available in
Q35TsegMbytesInitialization(), and set both PcdQ35TsegMbytes (for
OvmfPkg/SmmAccess) and "mQ35TsegMbytes" (for PlatformPei's own use)
accordingly. The new logic interfaces with the QEMU feature added in QEMU
commit 2f295167e0c4 ("q35/mch: implement extended TSEG sizes",
2017-06-08).

At this point we have to explicitly restrict Q35TsegMbytesInitialization()
to the Q35 board, but that's OK, because Q35TsegMbytesInitialization() is
only called when PcdSmmSmramRequire is set, and for that Q35 is already an
enforced requirement.

Cc: Jordan Justen <jordan.l.justen@intel.com>
Suggested-by: Jordan Justen <jordan.l.justen@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
---
 OvmfPkg/PlatformPei/Platform.h  |  2 +
 OvmfPkg/PlatformPei/MemDetect.c | 52 +++++++++++++++++++-
 OvmfPkg/PlatformPei/Platform.c  | 10 ++--
 3 files changed, 58 insertions(+), 6 deletions(-)

diff --git a/OvmfPkg/PlatformPei/Platform.h b/OvmfPkg/PlatformPei/Platform.h
index d2d627b221c4..ae855531c1b7 100644
--- a/OvmfPkg/PlatformPei/Platform.h
+++ b/OvmfPkg/PlatformPei/Platform.h
@@ -104,8 +104,10 @@ extern EFI_BOOT_MODE mBootMode;
 
 extern BOOLEAN mS3Supported;
 
 extern UINT8 mPhysMemAddressWidth;
 
 extern UINT32 mMaxCpuCount;
 
+extern UINT16 mHostBridgeDevId;
+
 #endif // _PLATFORM_PEI_H_INCLUDED_
diff --git a/OvmfPkg/PlatformPei/MemDetect.c b/OvmfPkg/PlatformPei/MemDetect.c
index 886d23622665..97f3fa5afcf5 100644
--- a/OvmfPkg/PlatformPei/MemDetect.c
+++ b/OvmfPkg/PlatformPei/MemDetect.c
@@ -15,24 +15,27 @@ Module Name:
   MemDetect.c
 
 **/
 
 //
 // The package level header files this module uses
 //
+#include <IndustryStandard/Q35MchIch9.h>
 #include <PiPei.h>
 
 //
 // The Library classes this module consumes
 //
+#include <Library/BaseLib.h>
 #include <Library/BaseMemoryLib.h>
 #include <Library/DebugLib.h>
 #include <Library/HobLib.h>
 #include <Library/IoLib.h>
 #include <Library/PcdLib.h>
+#include <Library/PciLib.h>
 #include <Library/PeimEntryPoint.h>
 #include <Library/ResourcePublicationLib.h>
 #include <Library/MtrrLib.h>
 #include <Library/QemuFwCfgLib.h>
 
 #include "Platform.h"
 #include "Cmos.h"
@@ -45,15 +48,62 @@ STATIC UINT32 mS3AcpiReservedMemorySize;
 STATIC UINT16 mQ35TsegMbytes;
 
 VOID
 Q35TsegMbytesInitialization (
   VOID
   )
 {
-  mQ35TsegMbytes = PcdGet16 (PcdQ35TsegMbytes);
+  UINT16        ExtendedTsegMbytes;
+  RETURN_STATUS PcdStatus;
+
+  if (mHostBridgeDevId != INTEL_Q35_MCH_DEVICE_ID) {
+    DEBUG ((
+      DEBUG_ERROR,
+      "%a: no TSEG (SMRAM) on host bridge DID=0x%04x; "
+      "only DID=0x%04x (Q35) is supported\n",
+      __FUNCTION__,
+      mHostBridgeDevId,
+      INTEL_Q35_MCH_DEVICE_ID
+      ));
+    ASSERT (FALSE);
+    CpuDeadLoop ();
+  }
+
+  //
+  // Check if QEMU offers an extended TSEG.
+  //
+  // This can be seen from writing MCH_EXT_TSEG_MB_QUERY to the MCH_EXT_TSEG_MB
+  // register, and reading back the register.
+  //
+  // On a QEMU machine type that does not offer an extended TSEG, the initial
+  // write overwrites whatever value a malicious guest OS may have placed in
+  // the (unimplemented) register, before entering S3 or rebooting.
+  // Subsequently, the read returns MCH_EXT_TSEG_MB_QUERY unchanged.
+  //
+  // On a QEMU machine type that offers an extended TSEG, the initial write
+  // triggers an update to the register. Subsequently, the value read back
+  // (which is guaranteed to differ from MCH_EXT_TSEG_MB_QUERY) tells us the
+  // number of megabytes.
+  //
+  PciWrite16 (DRAMC_REGISTER_Q35 (MCH_EXT_TSEG_MB), MCH_EXT_TSEG_MB_QUERY);
+  ExtendedTsegMbytes = PciRead16 (DRAMC_REGISTER_Q35 (MCH_EXT_TSEG_MB));
+  if (ExtendedTsegMbytes == MCH_EXT_TSEG_MB_QUERY) {
+    mQ35TsegMbytes = PcdGet16 (PcdQ35TsegMbytes);
+    return;
+  }
+
+  DEBUG ((
+    DEBUG_INFO,
+    "%a: QEMU offers an extended TSEG (%d MB)\n",
+    __FUNCTION__,
+    ExtendedTsegMbytes
+    ));
+  PcdStatus = PcdSet16S (PcdQ35TsegMbytes, ExtendedTsegMbytes);
+  ASSERT_RETURN_ERROR (PcdStatus);
+  mQ35TsegMbytes = ExtendedTsegMbytes;
 }
 
 
 UINT32
 GetSystemMemorySizeBelow4gb (
   VOID
   )
diff --git a/OvmfPkg/PlatformPei/Platform.c b/OvmfPkg/PlatformPei/Platform.c
index b8a28450d6c5..98cfaaa28ed1 100644
--- a/OvmfPkg/PlatformPei/Platform.c
+++ b/OvmfPkg/PlatformPei/Platform.c
@@ -641,32 +641,32 @@ InitializePlatform (
   }
 
   S3Verification ();
   BootModeInitialization ();
   AddressWidthInitialization ();
   MaxCpuCountInitialization ();
 
+  //
+  // Query Host Bridge DID
+  //
+  mHostBridgeDevId = PciRead16 (OVMF_HOSTBRIDGE_DID);
+
   if (FeaturePcdGet (PcdSmmSmramRequire)) {
     Q35TsegMbytesInitialization ();
   }
 
   PublishPeiMemory ();
 
   InitializeRamRegions ();
 
   if (mXen) {
     DEBUG ((EFI_D_INFO, "Xen was detected\n"));
     InitializeXen ();
   }
 
-  //
-  // Query Host Bridge DID
-  //
-  mHostBridgeDevId = PciRead16 (OVMF_HOSTBRIDGE_DID);
-
   if (mBootMode != BOOT_ON_S3_RESUME) {
     if (!FeaturePcdGet (PcdSmmSmramRequire)) {
       ReserveEmuVariableNvStore ();
     }
     PeiFvInitialization ();
     MemMapInitialization ();
     NoexecDxeInitialization ();
-- 
2.13.1.3.g8be5a757fa67


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