[PATCH 1/1] ArmPlatformPkg/PrePi: replace set/way cache ops with by-VA ones

["Ard Biesheuvel" <ard.biesheuvel@linaro.org>]

Cache maintenance operations by set/way are only intended to be used
in the context of on/offlining a core, while it has been taken out of
the coherency domain. Any use intended to ensure that the contents of
the cache have made it to main memory is unreliable, since cacheline
migration and non-architected system caches may cause these contents
to linger elsewhere, without being visible in main memory once the
MMU and caches are disabled.

In KVM on Linux, there are horrid hacks in place to ensure that such
set/way operations are trapped, and replaced with a single by-VA
clean/invalidate of the entire guest VA space once the MMU state
changes, which can be costly, and is unnecessary if we manage the
caches a bit more carefully, and perform maintenance by virtual
address only.

So let's get rid of the call to ArmInvalidateDataCache () in the
PrePeiCore startup code, and instead, invalidate the UEFI memory
region by virtual address, which is the only memory region we will
be touching with the caches and MMU both disabled and enabled.
(This will lead to data corruption if data written with the MMU off
is shadowed by clean, stale cachelines that stick around when the
MMU is enabled again.)

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
 ArmPlatformPkg/PrePi/PeiMPCore.inf  | 1 +
 ArmPlatformPkg/PrePi/PeiUniCore.inf | 1 +
 ArmPlatformPkg/PrePi/PrePi.c        | 8 +++++---
 3 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/ArmPlatformPkg/PrePi/PeiMPCore.inf b/ArmPlatformPkg/PrePi/PeiMPCore.inf
index 9c5da0d42a7b..053f9fd9e616 100644
--- a/ArmPlatformPkg/PrePi/PeiMPCore.inf
+++ b/ArmPlatformPkg/PrePi/PeiMPCore.inf
@@ -37,6 +37,7 @@ [Packages]
 
 [LibraryClasses]
   BaseLib
+  CacheMaintenanceLib
   DebugLib
   DebugAgentLib
   ArmLib
diff --git a/ArmPlatformPkg/PrePi/PeiUniCore.inf b/ArmPlatformPkg/PrePi/PeiUniCore.inf
index ee9b05b25337..78d218ae09ca 100644
--- a/ArmPlatformPkg/PrePi/PeiUniCore.inf
+++ b/ArmPlatformPkg/PrePi/PeiUniCore.inf
@@ -37,6 +37,7 @@ [Packages]
 
 [LibraryClasses]
   BaseLib
+  CacheMaintenanceLib
   DebugLib
   DebugAgentLib
   ArmLib
diff --git a/ArmPlatformPkg/PrePi/PrePi.c b/ArmPlatformPkg/PrePi/PrePi.c
index 2bb144958139..254fb331733e 100644
--- a/ArmPlatformPkg/PrePi/PrePi.c
+++ b/ArmPlatformPkg/PrePi/PrePi.c
@@ -8,6 +8,7 @@
 
 #include <PiPei.h>
 
+#include <Library/CacheMaintenanceLib.h>
 #include <Library/DebugAgentLib.h>
 #include <Library/PrePiLib.h>
 #include <Library/PrintLib.h>
@@ -178,8 +179,6 @@ CEntryPoint (
 
   // Data Cache enabled on Primary core when MMU is enabled.
   ArmDisableDataCache ();
-  // Invalidate Data cache
-  ArmInvalidateDataCache ();
   // Invalidate instruction cache
   ArmInvalidateInstructionCache ();
   // Enable Instruction Caches on all cores.
@@ -200,6 +199,10 @@ CEntryPoint (
 
   // If not primary Jump to Secondary Main
   if (ArmPlatformIsPrimaryCore (MpId)) {
+
+    InvalidateDataCacheRange ((VOID *)UefiMemoryBase,
+                              FixedPcdGet32(PcdSystemMemoryUefiRegionSize));
+
     // Goto primary Main.
     PrimaryMain (UefiMemoryBase, StacksBase, StartTimeStamp);
   } else {
@@ -209,4 +212,3 @@ CEntryPoint (
   // DXE Core should always load and never return
   ASSERT (FALSE);
 }
-
-- 
2.20.1