ArmVirtPkg/QemuVirtMemInfoLib: use HOB not PCD to record the memory size

Due to the way we inherited the formerly fixed PCDs to describe the
system memory base and size from ArmPlatformPkg, we ended up with a
MemoryInit PEIM that relies on dynamic PCDs to communicate the size of
system memory between the constructor of one of its library dependencies
and the core module. This is unnecessary, and forces us to incorporate
the PCD PEIM as well, for no good reason. So instead, let's use a HOB.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

ArmVirtPkg/Library/QemuVirtMemInfoLib/QemuVirtMemInfoLib.c

@@ -6,10 +6,12 @@
 
 **/
 
-#include <Base.h>
+#include <Uefi.h>
+#include <Pi/PiMultiPhase.h>
 #include <Library/ArmLib.h>
 #include <Library/BaseMemoryLib.h>
 #include <Library/DebugLib.h>
+#include <Library/HobLib.h>
 #include <Library/MemoryAllocationLib.h>
 
 // Number of Virtual Memory Map Descriptors
@@ -24,6 +26,28 @@
 #define MACH_VIRT_PERIPH_BASE  0x08000000
 #define MACH_VIRT_PERIPH_SIZE  SIZE_128MB
 
+/**
+  Default library constructur that obtains the memory size from a PCD.
+
+  @return  Always returns RETURN_SUCCESS
+
+**/
+RETURN_STATUS
+EFIAPI
+QemuVirtMemInfoLibConstructor (
+  VOID
+  )
+{
+  UINT64  Size;
+  VOID    *Hob;
+
+  Size = PcdGet64 (PcdSystemMemorySize);
+  Hob  = BuildGuidDataHob (&gArmVirtSystemMemorySizeGuid, &Size, sizeof Size);
+  ASSERT (Hob != NULL);
+
+  return RETURN_SUCCESS;
+}
+
 /**
   Return the Virtual Memory Map of your platform
 
@@ -43,9 +67,16 @@ ArmVirtGetMemoryMap (
   )
 {
   ARM_MEMORY_REGION_DESCRIPTOR  *VirtualMemoryTable;
+  VOID                          *MemorySizeHob;
 
   ASSERT (VirtualMemoryMap != NULL);
 
+  MemorySizeHob = GetFirstGuidHob (&gArmVirtSystemMemorySizeGuid);
+  ASSERT (MemorySizeHob != NULL);
+  if (MemorySizeHob == NULL) {
+    return;
+  }
+
   VirtualMemoryTable = AllocatePool (
                          sizeof (ARM_MEMORY_REGION_DESCRIPTOR) *
                          MAX_VIRTUAL_MEMORY_MAP_DESCRIPTORS
@@ -59,7 +90,7 @@ ArmVirtGetMemoryMap (
   // System DRAM
   VirtualMemoryTable[0].PhysicalBase = PcdGet64 (PcdSystemMemoryBase);
   VirtualMemoryTable[0].VirtualBase  = VirtualMemoryTable[0].PhysicalBase;
-  VirtualMemoryTable[0].Length       = PcdGet64 (PcdSystemMemorySize);
+  VirtualMemoryTable[0].Length       = *(UINT64 *)GET_GUID_HOB_DATA (MemorySizeHob);
   VirtualMemoryTable[0].Attributes   = ARM_MEMORY_REGION_ATTRIBUTE_WRITE_BACK;
 
   DEBUG ((