ArmVirtPkg: remove PcdKludgeMapPciMmioAsCached

In ARM/AARCH64 guests that run on KVM, we can now use virtio-gpu-pci, so
PcdKludgeMapPciMmioAsCached is no longer necessary. Standard VGA continues
to work on TCG without the kludge.

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Ref: https://tianocore.acgmultimedia.com/show_bug.cgi?id=66
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>

ArmVirtPkg/ArmVirtPkg.dec

@@ -60,30 +60,6 @@
   gArmVirtTokenSpaceGuid.PcdTerminalTypeGuidBuffer|{0x65, 0x60, 0xA6, 0xDF, 0x19, 0xB4, 0xD3, 0x11, 0x9A, 0x2D, 0x00, 0x90, 0x27, 0x3F, 0xC1, 0x4D}|VOID*|0x00000007
 
 [PcdsFeatureFlag]
-  #
-  # "Map PCI MMIO as Cached"
-  #
-  # Due to the way Stage1 and Stage2 mappings are combined on Aarch64, and
-  # because KVM -- for the time being -- does not try to interfere with the
-  # Stage1 mappings, we must not set EFI_MEMORY_UC for emulated PCI MMIO
-  # regions.
-  #
-  # EFI_MEMORY_UC is mapped to Device-nGnRnE, and that Stage1 attribute would
-  # direct guest writes to host DRAM immediately, bypassing the cache
-  # regardless of Stage2 attributes. However, QEMU's reads of the same range
-  # can easily be served from the (stale) CPU cache.
-  #
-  # Setting this PCD to TRUE will use EFI_MEMORY_WB for mapping PCI MMIO
-  # regions, which ensures that guest writes to such regions go through the CPU
-  # cache. Strictly speaking this is wrong, but it is needed as a temporary
-  # workaround for emulated PCI devices. Setting the PCD to FALSE results in
-  # the theoretically correct EFI_MEMORY_UC mapping, and should be the long
-  # term choice, especially with assigned devices.
-  #
-  # The default is to turn off the kludge; DSC's can selectively enable it.
-  #
-  gArmVirtTokenSpaceGuid.PcdKludgeMapPciMmioAsCached|FALSE|BOOLEAN|0x00000006
-
   #
   # Pure ACPI boot
   #

ArmVirtPkg/ArmVirtQemu.dsc

@@ -100,9 +100,6 @@
   gEfiMdeModulePkgTokenSpaceGuid.PcdConOutGopSupport|TRUE
   gEfiMdeModulePkgTokenSpaceGuid.PcdConOutUgaSupport|FALSE
 
-  # Activate KVM workaround for now.
-  gArmVirtTokenSpaceGuid.PcdKludgeMapPciMmioAsCached|TRUE
-
 !if $(PURE_ACPI_BOOT_ENABLE) == TRUE
   gArmVirtTokenSpaceGuid.PcdPureAcpiBoot|TRUE
 !endif

ArmVirtPkg/ArmVirtQemuKernel.dsc

@@ -101,9 +101,6 @@
   gEfiMdeModulePkgTokenSpaceGuid.PcdConOutGopSupport|TRUE
   gEfiMdeModulePkgTokenSpaceGuid.PcdConOutUgaSupport|FALSE
 
-  # Activate KVM workaround for now.
-  gArmVirtTokenSpaceGuid.PcdKludgeMapPciMmioAsCached|TRUE
-
 [PcdsFixedAtBuild.common]
   gArmPlatformTokenSpaceGuid.PcdCoreCount|1
 !if $(ARCH) == AARCH64

ArmVirtPkg/PciHostBridgeDxe/PciHostBridge.c

@@ -365,8 +365,7 @@ InitializePciHostBridge (
                   );
   ASSERT_EFI_ERROR (Status);
 
-  MmioAttributes = FeaturePcdGet (PcdKludgeMapPciMmioAsCached) ?
-                   EFI_MEMORY_WB : EFI_MEMORY_UC;
+  MmioAttributes = EFI_MEMORY_UC;
 
   Status = gDS->AddMemorySpace (
                   EfiGcdMemoryTypeMemoryMappedIo,

ArmVirtPkg/PciHostBridgeDxe/PciHostBridgeDxe.inf

@@ -56,7 +56,6 @@
   gEfiMdePkgTokenSpaceGuid.PcdPciExpressBaseAddress
 
 [FeaturePcd]
-  gArmVirtTokenSpaceGuid.PcdKludgeMapPciMmioAsCached
   gArmVirtTokenSpaceGuid.PcdPureAcpiBoot
 
 [depex]