[PATCH v2 1/1] OvmfPkg/PlatformInitLib: q35 mtrr setup fix

["Gerd Hoffmann" <kraxel@redhat.com>]

Traditional q35 memory layout is 2.75 GB of low memory, leaving room
for the pcie mmconfig at 0xb0000000 and the 32-bit pci mmio window at
0xc0000000.  Because of that OVMF tags the memory range above
0xb0000000 as uncachable via mtrr.

A while ago qemu started to gigabyte-align memory by default (to make
huge pages more effective) and q35 uses only 2G of low memory in that
case.  Which effectively makes the 32-bit pci mmio window start at
0x80000000.

This patch updates the mtrr setup code accordingly.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
---
 OvmfPkg/Library/PlatformInitLib/MemDetect.c | 26 ++++++++++++++-------
 1 file changed, 18 insertions(+), 8 deletions(-)

diff --git a/OvmfPkg/Library/PlatformInitLib/MemDetect.c b/OvmfPkg/Library/PlatformInitLib/MemDetect.c
index 942eaf89cfcf..d1a4f4b20791 100644
--- a/OvmfPkg/Library/PlatformInitLib/MemDetect.c
+++ b/OvmfPkg/Library/PlatformInitLib/MemDetect.c
@@ -55,15 +55,25 @@ PlatformQemuUc32BaseInitialization (
   }
 
   if (PlatformInfoHob->HostBridgeDevId == INTEL_Q35_MCH_DEVICE_ID) {
-    //
-    // On q35, the 32-bit area that we'll mark as UC, through variable MTRRs,
-    // starts at PcdPciExpressBaseAddress. The platform DSC is responsible for
-    // setting PcdPciExpressBaseAddress such that describing the
-    // [PcdPciExpressBaseAddress, 4GB) range require a very small number of
-    // variable MTRRs (preferably 1 or 2).
-    //
+    LowerMemorySize = PlatformGetSystemMemorySizeBelow4gb (PlatformInfoHob);
     ASSERT (PcdGet64 (PcdPciExpressBaseAddress) <= MAX_UINT32);
-    PlatformInfoHob->Uc32Base = (UINT32)PcdGet64 (PcdPciExpressBaseAddress);
+    ASSERT (PcdGet64 (PcdPciExpressBaseAddress) >= LowerMemorySize);
+
+    if (LowerMemorySize <= BASE_2GB) {
+      // Newer qemu with gigabyte aligned memory,
+      // 32-bit pci mmio window is 2G -> 4G then.
+      PlatformInfoHob->Uc32Base = BASE_2GB;
+    } else {
+      //
+      // On q35, the 32-bit area that we'll mark as UC, through variable MTRRs,
+      // starts at PcdPciExpressBaseAddress. The platform DSC is responsible for
+      // setting PcdPciExpressBaseAddress such that describing the
+      // [PcdPciExpressBaseAddress, 4GB) range require a very small number of
+      // variable MTRRs (preferably 1 or 2).
+      //
+      PlatformInfoHob->Uc32Base = (UINT32)PcdGet64 (PcdPciExpressBaseAddress);
+    }
+
     return;
   }
 
-- 
2.37.3